We are currently in the process of rolling out a DID+SMS phone solution service based on FreePBX; we are in the beta tester stage but all looks great. We use VOIP.ms and the OpenSource SMS Connector Module see here: New open source SMS Connector module)
Currently it is working great when using the UCP and the Sangoma Talk App (Mobile or Desktop client.) We have only tested within Canada however VOIP>ms is promoting it will work in the USA. The SMS Connector does require API credentials from the Voip.ms account. The Install was very simple and it looks like others have contributed to the project and now supports multiple SIP vendors other then VOIP.ms.
If you are interested, I am happy to share how things are working for us.