Users of mobile phones that support the Global Standard for Mobile Communications (GSM) enjoy the flexibility of changing phones with a simple change of the GSM SIM card. T-Mobile users, however, sometimes find themselves wondering if they can alternate between a traditional post-paid calling plan and a pre-paid plan simply by changing the SIM card. With some basic understanding of the T-Mobile billing system, these users can quickly and conveniently change from plan to plan within minutes.
Programming is in the SIM
Unlike the code division multiple access (CDMA) phones used by competitors, where phone activation is based on the phone's electronic serial number and programmed into the carrier's switch, T-Mobile phones rely on the information stored in the mobile SIM card to activate service. These cards, once registered with T-Mobile central office equipment, control the functionality of the phone and contain vital information on the calling plan (whether the plan is post-paid or pre-paid, for example). As the SIM card is moved from phone to phone, the calling plan---along with other information, including any features associated with the plan and any stored contacts---follow the card to the new phone. If a pre-paid SIM is installed into a phone, regardless of its prior usage, the phone will function as a pre-paid device.
Some Phones are Locked
In general, all T-Mobile mobile phones will work with T-Mobile SIM cards, regardless of the type of plan associated with the SIM. Proprietary software on T-Mobile phones, however, prevent them with being used with SIM cards from other carriers. While a pre-paid SIM card serviced by T-Mobile may work without hassle in a T-Mobile phone, a SIM card activated and serviced by a competing company may cause the phone to go into an "out of service" condition. Likewise, other carriers often lock their own phones, preventing use of a T-Mobile pre-paid SIM card in their proprietary devices.
Some Phones Can Be Unlocked
If a user wants to use a competitor's SIM card in a T-Mobile phone, there may be a way to work around the proprietary programming that prevents this operation. Special software, available to cell phone professionals and software experts, can modify the programming inside a cell phone to remove restrictions placed by the carrier. In most cases, this "unlocking" function is legal and simply allows users to use the phone with another carrier. Some highly unique phones may use special software to make only certain features available in the "unlocked" mode, and other, typically less advanced, phones may disallow unlocking altogether. Still, if a user installs a T-Mobile pre-paid SIM card into a T-Mobile phone, or a competitor's pre-paid card into an unlocked T-Mobile phone, the phone will instantly become a pre-paid mobile device.
Tags: pre-paid card, T-Mobile phone, associated with, calling plan, card into, card T-Mobile, cell phone
