My experience is that many areas along San Diego's coast have weird deadzones because of its topography. When I was on Verizon, any time I went to the southernmost parts of Point Loma, my phone would roam to Tijuana and throw up warnings about extra charges for placing calls. There's no land mass between the lighthouse on Point Loma and TJ's hills.
Last week, on T-Mobile, I stumbled into a few spots along Sunset Cliffs that resulted in a complete drop of coverage. I suppose the center of Point Loma's hill blocks wherever the nearest tower is? I haven't noticed any fake palm trees in residential areas like that.
I used to work as a contractor on the base by the lighthouse, and can help explain this. The Navy is doing all kinds of radio experiments there, and (what I was told), it hugely impacts reception in the area.
