AT&T has a 700 MHz 4G LTE network, as does Verizon, but those networks aren’t interoperable because they use different blocks of spectrum. There’s a debate in the FCC right now as to whether operators should make their networks interoperable. It isn’t as easy as simply saying “make it so!”, there’s a lot of hardcore science involved with regards to antennas, filters, and power amplifiers. People said that it was going to be impossible to make a phone that supports multiple blocks of spectrum in the 700 MHz band, but Qualcomm has figured it out. In fact, they say that phones should be out by the end of the year that can handle three blocks of spectrum in bands below 1 GHz, three bands above that, and one ultra high frequency band such as the 2.5 GHz band that Clearwire owns. They go on to say that the FCC shouldn’t make interoperability mandatory, which is kind of strange when you think about it. If the FCC forced operators’ networks to play together, and Qualcomm was the only company that could make chips to make that happen, then wouldn’t they stand to make money hand over fist?
Anyway, all we know is that there’s a wider issue here regarding global 4G LTE roaming that no one is talking about. When it comes to 3G, Europe and Asia standardized on 2100 MHz and it’s worked out beautifully. More recently operators have decided to use some of their 900 MHz spectrum, which was meant for 2G networks, to build more robust 3G networks. That too is working out great. But 4G LTE is a whole other story. There’s the 800 MHz band, 2600 MHz band, some operators are using the 1800 MHz band, and there’s several other bands in between. If this isn’t figured out, think about how hard it’s going to be for Samsung, HTC, Apple, Nokia, etc., to release a 4G LTE phone that works globally.
It’s going to be a logistical nightmare keeping track of all those SKUs.
Additional Reading: Fierce Wireless