That is really interesting that their Bay Area network is full of holes. I have never used T-Mobile before in the Bay Area but would figure that the former Cingular Wireless would have done a better job building out that network.
Unfortunately, both the original PacBell and AT&T Wireless networks are both less than seamless T-Mobile street level coverage map being a lot more realistic than AT&T's shows that once you zoom out a little). It takes especially significant hit indoors, where signal varies widely. In my house it can go from -80dB down to -110dB (and then the phone loses the signal completely). At least T-Mobile seems to be patching up some of the holes, I noticed over the past year and a half their signal improving in two or three places where it used to be extremely weak. AT&T on the other hand has started to unwind T-Mobile roaming without any attempts to fill the void, so their coverage is also beginning to lag noticeably behind VZW.
You would think of all area's in the country CA would be top on their list to fill these voids, it would be like if they did the same in the NYC, Philly, Chicago & other big area's they didn't work on improving coverage. I can't figure out their thinking, other then I noticed on their recent news release's, they are starting some network buildouts & they all seem to give the impression they are just starting to do these projects & took a 6-9 month sabatical on these buildouts, during their mergers. Just like their 3G upgrades.
I was just in the Bay Area two months ago, and Verizon & Sprint have really done well with their coverage most everywhere I went, from Santa Cruz to Santa Rosa I'd say Verizon was a little better though, when it comes to Northern CA (where I also went, up near Mount Shasta). Some areas, however, such as Half Moon Bay only had Verizon or San Gregorio State Beach only had Sprint. Me, being an Alltel customer could use whatever was available Not sure about GSM coverage out there.
GSM coverage is kind of spotty, or rather striped AT&T towers and T-Mobile towers have some overlap but in a lot of places it's either one or the other. From what I can tell VZW has the best coverage in Bay Area.
Very interesting- I don't understand how carriers take away roaming before filling in their coverage holes. My guess is that too many people are roaming in AT&T dead spots and that they'd rather not pay roaming fees (and not have coverage in certain areas) until they get a tower of their own up. I know Verizon took some hits in some parts of the Bay Area after they removed Sprint as a roaming partner, but I think most of those holes have been fixed.
Beats me, especially considering that I have only noticed it on one LAC only, I can still roam on other nearby LACs.