-- Verizon became the first major U.S. carrier to adopt LTE (Long Term Evolution) last year and this week is rolling out its first LTE smartphone, the . LTE is essentially a bridge from such as HSPA and EV-DO Rev. A to the 4G IMT-Advanced technologies that the ITU has in mind. The company made its initial LTE launch in 38 markets covering roughly one-third of the U.S. population. The carrier plans to have its entire current 3G footprint upgraded to LTE by the end of 2013.

As far as speeds go, showed data downloads frequently topping 10Mbps in most major markets, although these tests were run when the network just started and didn't have much congestion to deal with. A by PC World showed that Verizon's LTE laptop air cards provided average download speeds of 6.5Mbps and average upload speeds of 5Mbps.

-- 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 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 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.