Actually, great news - there is an SMS solution for VOIP.ms, and I have it installed and it works just fine on my Android.

I'm an Android guy so I have no idea what's out there in the iPhone world, but check out an app called "VoIP.ms SMS" by Michael Kourlas. It took some minor configuring but it works great. I just give clients my Voip.MS number now and can respond to them no matter what SIM card I have, or where in the world I am.

The only limitation is that it doesn't send international texts, which is a solid bummer. But that's on VOIP.MS, not the app.