Since I'm in Major Metropolitan area (San Diego & Los Angeles, CA.) I don't have to worry about coverage issues, plus my AT&T iPhone 4S will work on T-Mo's 4G HSPA+ network
are you sure about that? unless t-mobile refarmed their network in LA, you would not get HSPA+ on iPhone 4S.
I thought only newer iPhone 5 with patched base band that capability? (For AWS spectrum)