Remember CDPD? WiMAX? Here's a look back at network technologies that came and went

As technologies evolve and new standards emerge, it's inevitable that the wireless industry will need to retire old technologies. Just last month, T-Mobile US (NYSE:TMUS) shut down MetroPCS' legacy CDMA network, and AT&T Mobility (NYSE: T) will do the same in September for the CDMA network it acquired from Leap Wireless.

More than 100 operators still maintain active CDMA networks and some plan to maintain them for the foreseeable future. Verizon (NYSE: VZ) has told its M2M customers that it plans to maintain CDMA technology through 2021. For others, it's more economical to shut them down, similar to other technologies that have seen better days. For a list of some of the more notable network retirements, check out this FierceWireless special report.