SIPTrunk does not have a template built-in to 3CX and the custom template they offer does not support SMS. You may want to look at one of the other companies in the BCM ecosystem.
Their sales guy, Kevin, is awesome but, for us, that did not overcome the severe issues with their services from the start. Our customer does 850,000 minutes per month and apparently that was not big enough to get any useful help from their support (lots of timeouts, rejects, etc.). They suggested that our DIDs were being blocked because they had been flagged by other carriers as spam.
We had to move to another provider on an emergency basis because we couldn't get the help we needed. All the issues instantly disappeared when we changed trunks (so much for the argument that the DIDs had been flagged as spam). Obviously, it was not our server, or internet connection, or setup etc. We swapped out the trunk an everything worked perfectly unchanged.