-- AT&T and T-Mobile both use HSPA+, an advanced version of the GSM-based 3G HSPA standard that delivers significantly higher speeds than its predecessor. Whereas older HSPA networks would typically deliver mobile download speeds of under 1Mbps, tests have generally delivered download speeds in the 2Mbps to 4Mbps range. So although HSPA+ may not represent as big a leap forward for mobile data as LTE, it is still a vast improvement over older 3G networks such as EV-DO and HSPA.
The two carriers decided to upgrade their 3G footprints with HSPA+ technology before they take the plunge into LTE over the next two years. AT&T, which said in January that it would be launching more than 20 "4G" devices this year, is planning a limited rollout of commercial LTE services this summer. T-Mobile is expected to start offering LTE services sometime in 2012.
-- Sprint and its partners at Clearwire are the only major players in the wireless industry to have adopted WiMAX as their technology of choice. Their current coverage extends to all major markets and covers more than 120 million points of presence. On average, WiMAX services deliver download speeds of between 3Mbps and 6Mbps, although PC World found in their tests that the network was not available on a consistent basis and also that the speeds of Sprint's 3G EV-DO Rev. A network had actually decreased over the past year.
Sprint has toyed with the idea of adopting LTE to supplement its WiMAX services, as both it and Clearwire would together have enough spectrum to support both technologies if they so desired. The companies will also likely roll out the 802.16m ("WiMAX 2") standard at some point, although that might not occur until 2013 since device certification for the standard is slated to start this year and it will take some time for carriers to commercially deploy the new technology over their existing networks.
Conclusion: Buying "4G services" from a carrier really doesn't tell you anything about its coverage or overall quality. Verizon's LTE network currently offers the fastest data rates of all the networks, although it isn't yet available throughout the entire country and its 3G backup network is significantly slower. T-Mobile and AT&T are currently getting good mileage with their HSPA+ networks and they should remain competitive with Verizon as they start rolling out LTE over the next two years. Sprint's WiMAX network also gets good speeds, although there remains a good deal of uncertainty about the future of its partners at Clearwire.
Sign up for Computerworld eNewsletters.