Question about AT&T billing zip code versus "primary use" zip code.

I am interested in buying an iPhone and have an activation question. According to the AT&T website, my zipcode is listed as not being in a service area. However, there is AT&T service all around me and in parts of my zip code (but for some reason, maybe since the signal is spotty, it is listed as not covered). Anyway, I will primarily be using my iphone at work and on the road to work (which is 40 miles away and in a great coverage area). So my question is; will I be able to activate my iPhone? I read somewhere that after you enter your billing zip code, if it is not eligible, you have an option of entering a "primary usage address". Is that correct? If so, I will simply use my employer's address if that is ok. Does anyone know about this and if this will work or not? I really don't want to go through the hassle of buying and returning if I am not going to be able to activate it. I already have a Verizon account that I am keeping because they have great coverage, but I want the cheapest AT&T account so I can use the iPhone for mostly web browsing while on the road and at work and while traveling.
FYI ( I will be using the iphone on AT&T's network, not roaming, so I am not worried about off network usage limits. There is AT&T coverage all around me, but just not in my particular zip code according to them. I live in the east Tennessee area between Knoxville and Chattanooga). Thanks for any advice and help.