My Voip.ms account is set up to send and receive SMS as SIP MESSAGE.
When I send a message from a cell phone TO Zoiper, it receives it, and I can answer. If I save this history to a new contact, I can even continue to communicate with this contact via SMS, and new messages to that number go to that contact's message history.
However, if I set up a different contact from scratch, give it the same number, same accounts in Advanced, and the rest exactly the same (except for the name of course) then I CANNOT send SMS to it, ever. It gives error 404, every time. When I set up the account and presence to "Contact Service Account" it doesn't even let me type in the message, but when I set it to the actual account name, it does let me try to send, but it does not succeed in sending.
I will look into your Sqlite database, to find out what exactly is different between those two contacts, but likely the UI for contact setup is not touching the relevant data, so it prevents the user from setting up the SMS capability for any contact except one set up starting from SMS history.