I've tried several searches to find any info on this problem but haven't come up with anything so I'm wondering if this is a new problem?

My Mom's Verizon Treo 600 (a refurb that just replaced a dead one a few weeks ago) has started to drop her outgoing audio on phone calls. It started intermittently but is getting more and more regular. Apparently the call begins alright, but after a varying amount of time the person on the other end can no longer hear her, though she can still hear them fine. She's forced to end the call and call them back to continue the conversation. Needless to say this is not very impressive for business customers, she's always apologizing for dropping calls these days. I'm about to demand another replacement 600 from Verizon, but I wanted to find out if this is a known issue first.