I've been having this problem as well. I setup the suggestion ports to forward directly to the Obi110, but I'm still getting dropped calls.
Here's a log from an incident that just happened. It was an incoming call that dropped after about 20 minutes. (the log starts with the call dropping), then they called back, I answered but couldn't hear them. They called back a third time, and the call dropped within about 2 minutes. I ended up just picking up my cell phone the next time using the T-Mobile USA Wi-Fi Calling app and didn't have any issues.
Aug 8 15:09:03 XMPP: Updating peer:jleonard.dtiglobal@gmail.com[TalkGadget2CC2B113] to online
Aug 8 15:10:04 XMPP: Updating peer:dtiglobal@thompson-web.org[android3d56f45f05c3] to online
Aug 8 15:12:02 XMPP: Updating peer:dtiglobal@thompson-web.org[android3d56f45f05c3] to online
Aug 8 15:13:38 GTALK: sess SIP1644278913@10.229.66.68 state changed from 5 to 6
Aug 8 15:13:38 RTP: Del Channel
Aug 8 15:13:38 [JB] call overall status -- #012peer: 74.125.127.126:19295(relay),#012local: 192.168.1.144:63826,#012pkt_tx: 106535,#012pkt_rx: 103576,#012bytes_tx: 18323552,#012bytes_rx: 17815072,#012clk_diff: 30 PPM,#012pkt_in_jb: 0,#012pkt_ooo: 17,#012pkt_lost: 51,#012pkt_late: 12,#012pkt_loss_rate: 0 %,#012pkt_drop_rate: 0 %,#012jb_len: 190 ms,#012curr_rcvd_jitter: 10 ms,#012rcvd_digits: 0,#012underruns: 12,#012overruns: 0,#012seq_num_broken: 57,#012pkt_interp: 5956,#012skew_comp: -40 ms,#012frm_in_pkt: 2
Aug 8 15:13:42 [SLIC]: Slic#0 HOOK FLASH
Aug 8 15:13:42 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:13:42 [CPT] --- FXS h/w tone generator (dial)---
Aug 8 15:13:45 [SLIC]: Slic#0 ONHOOK
Aug 8 15:13:45 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:13:49 [SLIC]: Slic#0 OFF HOOK
Aug 8 15:13:49 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:13:49 [CPT] --- FXS h/w tone generator (dial)---
Aug 8 15:13:52 [SLIC]: Slic#0 ONHOOK
Aug 8 15:13:52 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:14:26 TCP: Connect OK(HTTP GET)42
Aug 8 15:14:26 Update Config Now ...
Aug 8 15:14:26 XML_parse_prov 0
Aug 8 15:14:26 PARAM: Notification sent: 0
Aug 8 15:14:26 Same version: Skipped (2)
Aug 8 15:14:26 TCP: Connect OK(HTTP GET)44
Aug 8 15:14:26 Update Config Now ...
Aug 8 15:14:26 XML_parse_prov 0
Aug 8 15:14:26 PARAM: Notification sent: 0
Aug 8 15:14:26 Same version: Skipped (2)
Aug 8 15:14:26 We will check new config in 3600 s
Aug 8 15:14:44 GTALK: sess SIP1559229106@10.13.171.13 state changed from 0 to 3
Aug 8 15:14:44 [SLIC] CID to deliver: ''
Aug 8 15:14:44 GTT: call state changed from 0 to 5
Aug 8 15:14:44 GTALK: sess SIP1559229106@10.13.171.13 state changed from 3 to 4
Aug 8 15:14:45 GTALK: Candidate 4a7d7f7e:443(5);2 2
Aug 8 15:14:45 GTALK: Candidate 4a7d7f7e:19294(6);2 1
Aug 8 15:14:45 GTALK: Candidate 4a7d7f7e:19295(10);2 0
Aug 8 15:14:45 GTALK: Total peer candidates:3
Aug 8 15:14:49 [SLIC]: Slic#0 OFF HOOK
Aug 8 15:14:49 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:14:49 GTALK: sess SIP1559229106@10.13.171.13 state changed from 4 to 5
Aug 8 15:14:49 RTP: Connecting->4a7d7f7e:443
Aug 8 15:14:49 GTT: call state changed from 5 to 3
Aug 8 15:14:49 TCP: Connect OK(rtpssl)48
Aug 8 15:14:49 RTP: Start->4a7d7f7e:19295(80);0;0;0:0:0;1(47)
Aug 8 15:14:49 RTP: Skt Connected
Aug 8 15:14:50 RTP: PeerRflxAddr=4a7d7f7e:19295
Aug 8 15:15:04 [SLIC]: Slic#0 ONHOOK
Aug 8 15:15:04 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:15:04 GTALK: sess SIP1559229106@10.13.171.13 state changed from 5 to 6
Aug 8 15:15:04 RTP: Del Channel
Aug 8 15:15:04 [JB] call overall status -- #012peer: 74.125.127.126:19295(relay),#012local: 192.168.1.144:56372,#012pkt_tx: 758,#012pkt_rx: 72,#012bytes_tx: 129908,#012bytes_rx: 12224,#012clk_diff: 0 PPM,#012pkt_in_jb: 0,#012pkt_ooo: 0,#012pkt_lost: 0,#012pkt_late: 0,#012pkt_loss_rate: 0 %,#012pkt_drop_rate: 0 %,#012jb_len: 190 ms,#012curr_rcvd_jitter: 0 ms,#012rcvd_digits: 0,#012underruns: 0,#012overruns: 0,#012seq_num_broken: 0,#012pkt_interp: 1356,#012skew_comp: 0 ms,#012frm_in_pkt: 2
Aug 8 15:15:08 [SLIC]: Slic#0 OFF HOOK
Aug 8 15:15:08 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:15:08 [CPT] --- FXS h/w tone generator (dial)---
Aug 8 15:15:11 [SLIC]: Slic#0 ONHOOK
Aug 8 15:15:11 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:15:50 GTALK: sess SIP510907621@10.229.66.68 state changed from 0 to 3
Aug 8 15:15:50 [SLIC] CID to deliver: ''
Aug 8 15:15:50 GTT: call state changed from 0 to 5
Aug 8 15:15:50 GTALK: sess SIP510907621@10.229.66.68 state changed from 3 to 4
Aug 8 15:15:51 GTALK: Candidate 4a7d7f7e:443(5);2 2
Aug 8 15:15:51 GTALK: Candidate 4a7d7f7e:19294(6);2 1
Aug 8 15:15:51 GTALK: Candidate 4a7d7f7e:19295(10);2 0
Aug 8 15:15:51 GTALK: Total peer candidates:3
Aug 8 15:15:57 [SLIC]: Slic#0 ONHOOK
Aug 8 15:15:57 [SLIC]: Slic#0 OFF HOOK
Aug 8 15:15:57 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:15:57 GTALK: sess SIP510907621@10.229.66.68 state changed from 4 to 5
Aug 8 15:15:57 RTP: Connecting->4a7d7f7e:443
Aug 8 15:15:57 GTT: call state changed from 5 to 3
Aug 8 15:15:57 TCP: Connect OK(rtpssl)51
Aug 8 15:15:57 RTP: Start->4a7d7f7e:19295(80);0;0;0:0:0;1(50)
Aug 8 15:15:57 RTP: Skt Connected
Aug 8 15:15:58 RTP: PeerRflxAddr=4a7d7f7e:19295
Aug 8 15:17:00 GTALK: sess SIP510907621@10.229.66.68 state changed from 5 to 6
Aug 8 15:17:00 RTP: Del Channel
Aug 8 15:17:00 [JB] call overall status -- #012peer: 74.125.127.126:19295(relay),#012local: 192.168.1.144:47838,#012pkt_tx: 3122,#012pkt_rx: 2064,#012bytes_tx: 536516,#012bytes_rx: 354848,#012clk_diff: 80 PPM,#012pkt_in_jb: 0,#012pkt_ooo: 0,#012pkt_lost: 0,#012pkt_late: 0,#012pkt_loss_rate: 0 %,#012pkt_drop_rate: 0 %,#012jb_len: 190 ms,#012curr_rcvd_jitter: 7 ms,#012rcvd_digits: 0,#012underruns: 0,#012overruns: 0,#012seq_num_broken: 0,#012pkt_interp: 2107,#012skew_comp: 0 ms,#012frm_in_pkt: 2
Aug 8 15:17:03 [SLIC]: Slic#0 HOOK FLASH
Aug 8 15:17:03 [SLIC] CID to deliver: '(null)' (null)
Aug 8 15:17:03 [CPT] --- FXS h/w tone generator (dial)---