That crazy hybrid satellite / terrestrial mobile phone network being erected by start-up TerreStar just got a nice boost by signing a reciprocal roaming agreement with a rather sizable partner: a scrappy little carrier going by the name AT&T. Recent releases on TerreStar's site indicate that its first satellite won't be ready to launch until April of next year -- a bit of a delay from the end of 2008 estimate they'd been suggesting before -- but at least they'll be riding on the coattails of a nice, fat footprint on the ground when the time comes to flip the switch.