Changing your SIM card to another phone is an easy process, but not all phones will work with your carrier. Here are a few tips you will need to know when choosing to use a new phone with your SIM card.
Compatible Phones
Each carrier offers different calling frequencies. For instance, AT&T uses the 850 Mhz option while T-Mobile uses the 1900 Mhz frequency. Make sure the phone you're switching to supports the calling frequency of your carrier.
Unlocked Phones
Many carriers lock their phones to their own service, therefore an AT&T Sim card will not work in a T-Mobile cell phone. Unlocked cell phones, however, are not tied to a carrier and will work with any carrier if the phone supports the proper frequency.
Unlock Your Locked Cell Phone
If you have a locked phone for one carrier and you want to move it to a new carrier, you'll need to ask your carrier for the cell phone's "unlock code" or purchase an unlock code online. Most carriers will provide unlock codes after 90 days of continuous service.
GSM Carriers
Only GSM carriers such as AT&T Wireless and T-Mobile support SIM card-based devices, while CDMA carriers such as Verizon and Sprint use ESN Numbers to identify their phones, and do not require or accept SIM cards.
Considerations
Quad-Band GSM devices support the 850/900/1800/1900 Mhz calling frequencies and will typically work anywhere in the world through hundreds of carriers.
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