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Pre-Owned Devices: Deciphering Network Compatibility

Choosing which network-associated devices to stock in your store can vary by region, population, and demographic; and carrier capability isn’t always as easy as CDMA or GSM. How can you tell which locked/unlocked devices will work with what carrier? We’ve created this blog post to guide and help navigate the world of network compatibility, and clarify some of the confusion surrounding carriers, data, and service unlocking.

Cellular data service runs on two main networks, CDMA and GSM. Phones that use GSM networks utilize a SIM card to identify a customer's account, phone number, and selected service, while CDMA uses electronic serial numbers for identification. These two networks have generally been incompatible across devices. However, since the launch of LTE networks in 2010, compatibility between CDMA and GSM carriers have been much easier. LTE allows CDMA and GSM unlocked models to accept service across networks, blurring the line on which devices are compatible. This creates a vague and confusing relationship between all device models, and their wireless providers.

What is LTE?

4G (fourth generation) refers to the frequency band that measures the range and density of a signal. LTE (Long-Term Evolution) is a term coined to describe the efficiency of wireless communications across data networks. It is a transmit-receive path followed to achieve 4G data speeds. 4G LTE is now the standard for high speed wireless communications, and is used by all major wireless providers. It improves download speeds from traditional 3G networks can provide.

The basis of LTE is that both CDMA and GSM networks are built on GSM technology, and LTE allows for cross-compatibility between the two. Unlike pre-LTE models, many carriers will work across different devices, regardless of network association and SIM.

While this function has been utilized in the Euro and Asian markets for a number of years, LTE is relatively new to the US. Major carriers in the US include Sprint, Verizon, T Mobile, and AT&T. Each major carrier has a variety of smaller, regional brands, or MVNO’s (Mobile Virtual Network Operators) that fall under their respective umbrellas. All major carriers run off of either CDMA, or GSM protocols for data.

These two networks break down like this:


The major domestic carriers currently using CDMA networks are Verizon, Sprint, and US Cellular. In the past, phones on these networks had extremely limited compatibility, even across other CDMA carriers. This was before the use of LTE. Since it’s implementation into the market, devices have grown more and more compatible, making newer models more carrier-flexible than even previous LTE models.

For the iPhone, LTE network models started with the iPhone 5. Since then, iPhone 5c, 5s, SE, 6, 6s, 7, and all Plus models use LTE, and supported networks. US Cellular customers may be able to use these phones as well (Verizon unlocked/non-AT&T GSM unlocked). Out of these, iPhone 6s and 7 series may be the first true universal models available in the US, and are designed to be cross-compatible with any carrier.

For a complete list of Android phones that use LTE, refer here.

All of the certified pre-owned devices we stock that are available for Verizon have been unlocked, meaning they are not held down to strictly Verizon, but were given permission by Verizon to accept other CDMA network carriers. If you have a Sprint device, chances are slim that it will transition easily if you’re trying to switch it to Verizon. The spectrum bands are incompatible, and Verizon is unlikely to accept a Sprint branded phone. Sprint does, however, have a very long list of MVNO’s, like Boost Mobile, CellNUVO, and Virgin Mobile, which sell well in some parts of the country. Of course, there are exceptions to every rule when it comes to device compatibility, and it is best to contact the carrier for specifics, in particular when dealing with a Sprint device.


AT&T and T-Mobile are the two main wireless services using GSM. There are also many MVNO’s that are subsets of these providers. Examples include Straight Talk (also compatible with Sprint locked), Metro PCS, and Centennial wireless, among many others.

T Mobile SIM cards are compatible with only AT&T unlocked and GSM unlocked devices, along with Verizon unlocked, as long as the device is LTE. While unlocking an AT&T device is similar to Sprint because obtaining permission from AT&T to switch service is required, it isn’t quite as difficult. Again, while GSM has traditionally been the easier network to unlock and switch service, there are exceptions to every rule, and the only way to know for sure is to contact the service provider.

Choosing a Device for Your Area

Most devices can be cross-compatible on GSM or CDMA networks if the models are LTE. General exceptions are AT&T and Sprint locked, as they are largely relegated to their own subsect regional brands. It is always a good idea to double-check with the carrier before stocking or special ordering devices, to make sure that the locked/unlocked models you’re buying will work on popular networks in your area. Websites like willmyphonework.com and gsmarena.com are also useful resources for determining which services will work with a device, especially in terms of smaller, regional carriers.

Improving customer experience and increasing profits can be as easy as keeping a selection of devices in stock. From possible upgrades, to new pre-paid activation, to replacements for irreparable issues (water damage, board damage, etc), adding devices to your list of services will ensure that every customer gets the best possible solution, and nobody leaves empty handed.

For more information on device compatibility and network services, contact your dedicated account representative today, and be sure to stay tuned here for more helpful guides and information on how to increase your bottom line, and drive business!