Questions to consider in deciphering 4G technology

— -- As a marketing campaign, "Can you hear me now?" is so yesterday.

For wireless carriers, fat profit margins are found in data, especially in videos and heavy business files that drive subscribers to spend more time on their phones.

U.S. wireless carriers have spent billions in building a new generation of network to handle the traffic onslaught. Called 4G (short for "fourth generation"), it is faster than the current 3G standard for data networks, and is rolling out gradually throughout the country. Phone manufacturers are also introducing a handful of new models that run on the fastest networks.

But despite heavy advertising, customers are still befuddled by the changes, made all the more complex by a flood of industry jargon and acronyms, says Berge Ayvazian, editor at 4G Trends. "You have no idea how much confusion is out there," he says.

Here are some questions to consider when upgrading to a 4G phone.

Q: How fast is 4G?

A: In theory, a fast 4G network can download 5 megabits to 20 megabits of data per second, says Roger Entner, an industry analyst at Recon Analytics. A 3G network typically downloads at about 1 Mb or less in that time frame. A large photo file is about 1 Mb.

There is considerable debate on the minimal speed required for a 4G network. The International Telecommunications Union, the industry's authoritative body in Geneva, has never specified the speed requirement, Entner says. "The (carriers') marketing department won. And the consumer is very confused."

4G networks are undoubtedly faster. But various factors can worsen performance, including network traffic, phone type, your proximity to a cell tower for the shorter wireless part of your call and the quality of the way traffic is directed across the wired lines of the network, where much of the data transmission takes place.

Q: What are the different types of 4G?

A: Carriers have a loose definition of 4G.

Independent analysts agree that the fastest 4G network is Long-Term Evolution (or LTE), which is being installed by both Verizon Wireless and AT&T. T-Mobile announced Thursday that it will invest $4 billion in building out a 4G LTE network.

The peak user rate for downloading data on LTE networks — best cases, in other words — can range from 6.5 Mb to 26.3 Mb per second, says industry group 4G Americas.

Verizon has the largest LTE network, available in about 190 U.S. markets.

AT&T's LTE, which is about a year old, is available in 28 markets. For non-LTE markets, AT&T runs a slower 4G standard called HSPA+ (High-Speed Packet Access), enhanced from the existing 3G network. The peak download speed of the HSPA+ used by AT&T can range from 1.9 Mb to 8.8 Mb per second, 4G Americas says. Peak speeds for T-Mobile's variety of HSPA+ ranges from 3.8 Mb to 17.6 Mb per second, it says.

Sprint uses yet another 4G standard called WiMax (Worldwide Interoperability for Microwave Access). Entner considers it a "dead-end technology." Peak speed ranges from 1 Mb to 5 Mb per second, 4G Americas says. Sprint plans to introduce its LTE network later this year.

Q: Will my 3G phone work in a 4G network?

A: Yes, but not at 4G speed. And on a 3G network, a 4G phone works only at 3G speed.

Q: Are all 4G phones pretty similar?