Thank you for the battery suggestion. I placed new batteries in both handsets -- the one connected to PhonePower and the one connected to GV. Today on my conference call, the PhonePower call dropped at 63m and after I called back, again at 48m. I called back again with the GV handset and had no real issues (two times with GV the client said they couldn't hear me, but I could still hear them. I assume I had just covered up the handset mic and the call continued on).
I did learn something important though: Although on my end the call just goes silent and doesn't disconnect to a dial tone, apparently the call does actually disconnect. I learned this when my conference call participants on the other end of the line told me that they knew the phone died because the conference service broadcast a message saying they were the only participant left on the call. This might indicate a different issue than just going silent.
In addition to changing to new batteries in both handsets, I replaced the CAT-5 cable between the modem and the router, updated the OBI firmware, and made sure (again) everything was fully plugged in and not too close together.
Since the spontaneous call drops have happened with both PhonePower and GV (although the problem today was with PP only), should I assume the problem is with the Obi? I'm getting desperate to fix this issue since I have these calls 2-3 times per week for the next several weeks, and they last 4 hours each. I have another call with this same client on Monday. I can't have the calls keep dropping over and over and over...
I welcome any suggestions. Thanks.