FAQ: Cellular Carriers and Compatibility

How they can send information to your phone without using a tethered soup can is confusing enough, but the compatibility of GSM and CDMA data technologies with certain phones can be even more baffling. Check out this FAQ to learn the basics of these cellular-data standards and find a phone that will work under either one.

Q: What’s the difference between GSM and CDMA?

A: GSM and CDMA are two different technologies used by cellular carriers to transmit voice  and data to and from your phone. While the differences between the two are highly technical, GSM and CDMA carriers all largely provide the same services: phone plans with high-speed mobile data, voice, and text. The primary feature distinguishing these two technologies is that they’re not cross-compatible. If you have a GSM phone, it has to be used with a GSM carrier; likewise for CDMA phones and carriers.

Q: What does “GSM/CDMA Unlocked“ mean?

A: If you buy a phone from a carrier, it can only be used with that carrier. AT&T locked phones can only be used on AT&T’s network, for example. If you buy an unlocked phone, though, it can be used with any carrier that supports a wireless technology compatible with the phone’s. For GSM, that includes carriers such as AT&T and T-Mobile. CDMA carriers include Verizon and Sprint. Click here for a complete list of GSM and CDMA carriers.

Q: Do GSM/CDMA smartphones work internationally?

A: If you have cellular service with a US-based carrier, international service depends on the details of your specific plan. If you’re trying to activate service on an unlocked phone outside the US, however, there are GSM and CDMA carriers in most countries that can be used to activate a smartphone — it’s just a matter of finding one with a plan that best suits your needs. GSM is overwhelmingly used internationally.