Just got a call from Telus Mobility. There have been a rash of 700's come back because when party A called a Treo, the Treo's mic would cut out, and therefore the Treo could not be heard.

Turns out the the treo mic is not the problem, but the TTY setting.

Settings>Personal>Phone>TTY=Off solves the problem.

Hope this helps someone else with this issue.