Why will my 3G MicroCell not connect to my Time Capsule? The 3G MicroCell connects perfectly when directly plugged into the DSL modem but will not connect when plugged into the Time Capsule - Don't know if this is important but iMac is running OS X 10.8.4 with the new Airport Utility. ???
It's very possible that if you put the 3G microcell behind the Time Capsule (or any router), that you have to configure the router to forward or open up particular ports required by the Microcell to operate correctly. There is some information on the AT&T site for the Microcell they have, under "Specifications".