I have an office with 10 or so Yealink T48S behind and SBC that is having an odd call quality issue. I am pretty sure it is isolated to their office but I can't figure out what is causing it. This is what is happening..... 1) caller in office makes an outbound call to me on a non-3cx phone line. 2) we are talking just fine, very clear, sounds good.... 3) Then I can barely hear his voice... it is as if he has is hand over the receiver 4) He can hear me perfectly --- I can't really understand his words but can hear that he is talking. 5) After maybe 10 to 20 seconds, I can hear him again perfectly. 6) This might happen two or three times in a 5 to 10 minute phone call. He is not on speaker phone. He is calling from a new (purchased with the last month) Yealink T48S. Any ideas? Thank you for any help.