Current iPhone owners in the U.S. who are thinking about upgrading to a new iPhone to take advantage of the faster 3G network may wind up paying more for what they already have.

AT&T’s 3G coverage map reveals its 3G coverage is spotty, concentrated in major metropolitan areas around the country. We stitched together this map using the coverage tool from AT&T’s Web site. The dark blue patches indicate areas where the 3G network is available. For the vast majority of the country -- geographically, at least -- 3G is unavailable.

That means many new iPhone owners will be paying for 3G speeds they may never see. According to AT&T, there is only one data plan for the new phone: $30/month will get you 3G speeds where available; 2G (or EDGE) speeds elsewhere. Current iPhone owners pay $20/month for their data plan, which also includes 200 SMS messages (something that will cost new iPhone customers an additional $5.)

Few and far between: AT&T’s 3G network remains clustered in major metropolitan areas.

AT&T says its 3G network is growing quickly. "We are in 280 major metropolitan areas now and will be in 350 by the end of the year," AT&T’s Mark Siegel told The Mac Observer. Siegel, AT&T’s executive director of media relations, said the company thinks that "folks who buy the new iPhone have an excellent chance of being in an area our 3G network covers." Unless, that is (according to AT&T’s own map), they live in Iowa, Nebraska either of the Dakotas, Wyoming, Montana or the more rural areas of just about every other state in the union.

Of course, Siegel points out, "if you go to in an area that is 2G, the iPhone will work there as well." That’s likely to be little consolation to customers who don’t just go to areas with no 3G coverage, but live and work in them as well. For those customers, the 2G data plan has just effectively gone up by $10 a month ($15 if they still want 200 SMS messages per month.)

So, what’s an iPhone owner (or prospective owner) to do? For those who live in areas with good 3G coverage, the increased speed may be well worth the extra cost. For current iPhone owners not within AT&T’s 3G network, you may want to hang on to your old iPhone: unless GPS is critical to you, the 2.0 software update should give you everything else the new iPhone offers except the plastic back and metal buttons.

The news may be worst for those in non-3G areas who held off on buying a first-gen iPhone. They’ll be paying more for the same old EDGE speeds early adopters have been getting for a year. Even AT&T’s spokesperson seemed to have a hard time putting a positive spin on this one: "It is their call as to whether or not the iPhone 3G will meet their needs."

In the case of the iPhone, it could be a case of good things coming to those who don’t wait.