Any sort of antenna amplifier that didn't connect directly to your phone would essentially be another cell tower, i.e., a relay point. Wouldn't it?

We actually have something like this in our office. Apparently the previous tenants had enough pull with ATT to get them to put in some sort of relay. I don't really know what it is our how it works, but it is a relatively small box on the wall with a single antennae wire attached that runs somewhere (the roof?). Anyway, I don't know who makes it or what to really call it, but this type of device does exist.

-Mike