Inside the SME Voip web GUI, as soon as I click on the "start sip registration" and go to the sys log, this is what I get:
loc2 .Info 2018-09-05T14:34:02Z 173-[ SendFwuKillMail Succeeded]
loc7 .Info 2018-09-05T14:34:08Z 173-[ DECT MAC statistics: Pmid:00001 Typ:FN Res:0 Frames:1082,0,0 Bho:0,0 Rssi:56]
loc7 .Info 2018-09-05T14:34:10Z 173-[ Register 1712 for Line: 0]
loc3 .Info 2018-09-05T14:34:29Z 173-[ Registration of user 1712 (ExtId#0) on domain 10.64.195.12 failed]
loc2 .Info 2018-09-05T14:34:32Z 173-[ SendFwuKillMail Succeeded]
10.64.195.12 is the internal IP of the 250 phone system itself.