AT&T, for example, started calling its current upgraded HSPA+ network 4G instead of 3G. It's not the fastest major network in the country -- that's Verizon's LTE, based on advertised speeds -- but AT&T says it has a better transition path to its next-generation network.

"Today, we're seeing 4G on HSPA+ in markets with enhanced backhaul, with speeds up to 6Mbps," said Ralph de la Vega, AT&T Mobility's president and CEO, during his company's developers' summit held at CES.

"We have the best transition path to 4G and we're the only U.S. company with this plan," de la Vega said.

He is arguing that AT&T's plan is better than Verizon's because once AT&T starts launching LTE, users will be able to fall back onto the HSPA+ network, which can deliver as fast as 6 Mbps download speeds. At CES, AT&T said it will advance its timeline for rolling out LTE, with launches starting in the middle of this year.

Verizon, however, is going straight from its existing 3G network to LTE, without an interim step like HSPA+. That means users who aren't in the LTE coverage areas will drop down to Verizon's slower 3G EV-DO Rev. A (Evolution-Data Optimized) network, which offers download speeds of around 600 kbps to 1.4 Mbps.