If the issue is simply in-building signal strength, there are a number of antenna systems avaialble that can improve in-building coverage. You can either do a Google search for "Nextel home antennas" or find a local Nextel store that has been putting up in-building antennas for businesses. I've never used one, but I have heard some people speak highly of the Wilson brand; no endoresment on my part, just repeating what I've heard.
http://www.wilsoncellular.us/cell-phone-antennas-cel ... »
There are a lot of companies with products like this.
Regarding a true Airave-like syst...