In case this happens to anyone, I found a solution. I bought the "Panasonic KX-TG7875S Link2Cell Bluetooth Enabled Phone" from Amazon because Obihai recommended buying a Panasonic phone system using a base station. This phone system has a base unit that you plug directly into the Obihai device. Then, all the other phones connect to that base station wirelessly. That solved the line in use issue for me. This specific phone system has some useful features too.
I also had a problem where forwarded calls from my Google Voice number to my Callcentric number would cause the phones to ring weirdly and out of sync. This issue was because my Obi110 had set different ringtones for GV and CC. To fix...
1. Login your obi device on
obitalk.com2. Click on the settings icon under "My Obi Devices"
3. Click "Obi Expert Configuration" at the bottom
4. Click "Enter Obi Expert"
5. Expand the "Voice Service" section
6. Finally, Check what value "X_RingProfile" is under "SP1 Service" and "SP2 Service". Make sure that "X_RingProfile" setup for all of your SP Services are using the same letter(ringtone), for example "A".