I'm currently trying to set up voip.ms as a voip provider in 3CX using the instructions found here as a guideline: http://wiki.voip.ms/article/3CX_Phone_System This works fine if I'm setting it up with my main voip.ms account (e.g. 103154). However, when I tried to set it up with a sub account (e.g. 103154_3cx) I get the following validation message: "Please enter a valid external number". It appears that this field only allows digits to be entered and does not allow special characters (i.e. underscore) or letters. I was almost able to workaround this by entering the main account (e.g. 103154) for the External Number and the sub account (e.g. 103154_pbx) for the Authentication ID. It shows up on voip.ms as registered, but it shows up in 3CX as being unregistered and inbound calls do not go through. I think the problem with this workaround is that the main account (e.g. 103154) is currently registered using a different pbx on a different IP address and port. I checked the 3CXPhoneSystem.trace.log and found the following: From: "Unknown" <sip:Unknown@22.214.171.124>;tag=as7b697cde The 126.96.36.199 IP address (which I have modified) is a different IP address than what 3CX registers with. This IP address is the one my other pbx uses. So it appears that using the main account for the External Number field in 3CX causes voip.ms to get confused. Any suggestions on how to workaround this? Also, is this validation really needed on the External Number field? P.S. I'm planning on using CallCentric as my main account and voip.ms as a backup. It would simplify things if I could us a voip.ms sub account with 3CX during the transition from my current pbx to 3CX.