UMA experts help. access point distance issue

i am having an issue with UMA and no audio, but its very strange.

Setup: i have an outdoor wifi access point i recently installed. its an ubiquiti bullet2 with a 9dbi omni antenna. i have a blackberry 9700 and use UMA on the access point.

Problem:UMA functions perfectly from 1-300' from the access points, but beyond 400 feet or so things get weird.

at 400 feet or more, the blackberry shows great wifi signal. it can recieve texts and send them. it can place calls and recieve them, the only problem is there is no call audio! inside of 300 feet the audio works great, but farther than that nothing can be heard by either party. whats even weirder is the blackberry will continue the call as if nothing is wrong. the phone doesn't drop the call, it seems to not be aware the audio packets arent making it.

ideas?

ps if you havent heard of ubiquiti yet, go to UBNT.com and checkout the hardware. its awesome!

Maybe get a second router and turn it into a repeater? Or, can these be chained? Not bad, on the price point.