Almost as soon as the iPhone was released, Apple was being criticized for forcing users to go through the App Store to access applications, and for restricting applications available through the App Store. Apple’s defense of the App Store was that it ensured that all applications loaded by users onto Apple iPhones were safe for use, reducing the risk of spreading viruses or corrupting the software. Critics pointed out that applications which rivaled Apple products were not available, even though many were safe for use, and some critics simply disliked the idea of being told what they could and couldn’t download. As a result, shortly after the iPhone’s release, people were jailbreaking their phones and providing information to others who were interested in jailbroken phones.

A jailbroken phone is not the same thing as an unlocked phone. When a phone is unlocked, it means that it can work on any mobile network, and “unlocking” can refer to a wide variety of phones. When a phone is jailbroken, it specifically allows the user to install applications from sources outside the App Store. Should other producers of mobile phones follow Apple’s lead with the App Store, presumably innovative techies will figure out how to jailbreak them as well.

A number of guides to producing a jailbroken phone can be found online, with varying degrees of reliability. People who are not experienced may encounter problems following such guides, and they could damage their devices so that they can no longer be used in the process. The directions for jailbreaking also vary depending on which version of the phone someone is using, and which version of the software is being utilized, making it important to read them thoroughly before starting, and to confirm that the directions are appropriate for the phone in question.

Sites which provide information about iPhone hacks such as those which can produce a jailbroken phone usually come with extensive disclaimers warning users that they proceed at their own risk. People are reminded that they cannot take a jailbroken phone in for service or repairs, and that they may have difficulty updating the software on a jailbroken phone. Those who lack expertise in this area may want to spend some time reading forums and reputable tech sites to learn about the most likely sources of accurate instructions for jailbreaking a phone.

Many global SIM cards are prepaid. As a result, cell phone costs can be kept under control and travelers have the option to place and receive calls wherever they may go. With a global SIM card, cell phone users may enjoy a number of the same features that they’re accustomed to using with a domestic SIM card. General Packet Radio Service (GPRS), voice mail and Short Message Service (SMS) or text services can come included in a global SIM card package.

The features available will largely depend on the company from which a customer obtains a global SIM card. For example, some companies have a specific list of countries and territories in which the global SIM card can function. Others may allow their customers to use their minutes whenever and wherever they choose. Depending on company terms, customers may also enjoy free daily access, no monthly fees and minutes without expiration dates.

Tourists, international students or those who conduct business in various countries may find this mobile technology useful. Global SIM card holders may appreciate that some global SIM cards come bundled with a domestic phone number. This means that two numbers may be contained on the SIM card- one international phone number and one domestic phone number. This allows callers from within and outside of the subscriber’s home country to call the global SIM card user without having to experience extra charges.

Consumers should keep in mind that they will need to obtain an international cell phone capable of working in all countries if they want to use a global SIM. The types of international phones available include dual-band, tri-band and quad-band phones. To determine the suitability of a phone, cell phone users will have to consider their home country and the country to which they are traveling, since certain bands only work in specific countries. Many consumers opt for a tri-band phone that works on the 900, 1800 and 1900 MHz bands, as they work in North America, Europe, Asia Pacific and the Caribbean. True world travelers may instead select a quad-band phone that works on the 850, 900, 1800 and 1900 MHz bands because these phones will work in any country that operates on GSM except Japan and South Korea.

To use a GSM SIM card, a user will need an unlocked phone—that is, a phone that is able to use SIM cards from different phone carriers—that uses the GSM network and works at the frequency the destination country uses. In many European countries, that frequency is 900 MHz or 1800 MHz. A phone that uses the proper frequency is important because even if a phone can use the GSM network, if it is not on the correct frequency, it still won’t work. Once a user has an unlocked phone that will work with the GSM network as well as the correct frequency, he can use the GSM SIM card. This card allows the user to use the same phone number internationally, no matter which country he is in.

Having a GSM SIM card allows a person to use the same cell phone in different countries rather than having to buy a new SIM card or phone whenever they travel internationally. This is ideal for those who travel often or want to be able to use their phone while on vacation. Since the SIM card holds the user’s phone number and information, the chip can even be used on another person’s international phone, while still billing the owner of the SIM card. This allows a person to either buy a phone of his own or rent one from an appropriate carrier.

If a person does not have the appropriate phone for a GSM SIM card, it is possible to rent an international phone. This is possible because he can insert the chip in various phones and use them in different countries. The information stays with the SIM card so the user can simply pay a fee to use a compatible phone of his choice while traveling in a different country. This allows him to use the phone without paying his domestic carrier’s roaming charges. Renting a phone allows someone to get a phone when they do not wish to or are unable to use his phone overseas.

3G networks represent the natural evolution from previous standards. Increasingly cellular phones and handheld mobile devices have incorporated additional services to telephony. Today’s mobile devices offer high-speed World Wide Web access, emailing, messaging, video phone and multimedia services. People want to be able to watch streaming movies on their cellular phones, download and play music, store data and share files with other cellular users. 3G networks offer faster, slicker ways to do this.

3G networks have been in operation globally since December 2005 and are continuing to spread. Some telecommunication companies in the U.S., Canada, Asia and Europe use a flavor of 3G called W-CDMA (Wideband Code Division Multiple Access). Others use CDMA2000, a non-compatible, competing 3G standard that includes a small family of protocols. These are known as CDMA2000 1xRTT (1 times Radio Transmission Technology), CDA2000 EV-DO (Evolution Data Only), and CDMA EV-DV (Evolution Data/Voice). Two popular mobile carries that use CDMA technology are Sprint and Verizon.

If your mobile phone utilizes a subscriber identity module or SIM card, your carrier is using a GSM (Global System for Mobile communications) network. GSM networks make the switch to 3G networks by first incorporating a General Packet Radio Service (GPRS). From here the network can be converted to a Universal Mobile Telecommunications System (UMTS), a 3G standard sometimes referred to as 3GSM. Alternately the network can incorporate an Enhanced Data rates for GSM Evolution (EDGE) system, though some people consider EDGE a 2.75G system since it is slightly slower than other 3G networks.

In practical terms, if you are looking for a GSM mobile phone carrier and that carrier offers UMTS or EDGE, you know you are getting a 3G network. Alternately, if considering CDMA carriers, look for one of the CDMA2000 flavors mentioned earlier. Be alert for newer technologies as well. As you might have expected, there is already talk of 4G networks, and protocols will continue to evolve with time to define newer standards.

A successful duplication hinges on the a user’s ability to extract the SIM card’s IMSI (International Mobile Subscriber Identifier) and Authentication key (Ki). While a IMSI is relatively easy to identify, finding the Ki can prove to be much more difficult for the novice user. Separate devices and software programs may have to be used to decrypt the Ki.

Engaging in activities that can result in a SIM clone is illegal. In the 1990s, companies that provided cellular services recognized the problems that SIM cloning presented and began to take measures to thwart the SIM cloning business. New security measures such as embedding security operations make obtaining a SIM clone more difficult. Now, if a SIM card detects that cloning has been engaged, the SIM card can render itself inoperable. Whereas a few years ago cloning could be done by radio, those interested in obtaining SIM clone must now have physical access to the original SIM card.

Though SIM cloning was easier with older models of cell phones and can still be technically done today, successfully completing a cloning is very difficult for some and virtually impossible for most. Most of the technology currently available to facilitate cloning is meant to work only on older models of phones. Anti-tamper software on V2 of 3G SIM cards makes cloning new SIM cards and their corresponding devices a lost effort.

As attractive as obtaining a SIM clone may seem to individuals who desire to use two phones with one phone number, legal and technical difficulties should discourage any efforts to clone SIM cards. It should also be noted that though using a SIM clone can appear convenient in some respects, safety issues may also present themselves as a result of using the clone. Law enforcement agencies may find it difficult to reach an injured or distressed party if an emergency call is made by a phone using a clone. This is because clones compromise the GSM location-based service that SIM cards rely on.