Hello! Had a similar problem when talking to my wife (she's at college in the US while I'm in Korea! ack!). We both have recently updated our iPad2s to ios5. I could call her iPhone4 (upgraded to ios5) with no trouble, but when our iPad2s tried to connect, there would be a brief connect and then connection would be lost;;
I simply had her TURN OFF AND TURN ON her iPad2 and now everything is fine. We reasoned that, kinda like a desktop computer program, ya need to sometimes reboot (turn off and then on) the device. Hope this helps, really, cause caring fathers are a rarity in this age! Good on ya!
-Michael~