A wireless T1 system is one in which the customer is connected to the upstream provider with a wireless connection. Usually this takes the form of a 2.4 or 5.8 GHz radio link which (in the US, at least) do not need any further FCC licensing or approval.

They used to have a wireless T1 link at work when we were in the old building. It sucked though, because it needed an absolutely unobstructed line of sight. Even if something as small as a tree branch was blown in the path, the reflections created would slow the T1 to a crawl.