I am in Europe using my wifi-only tablet for texting via Rogers One Number. I also have my cell phone to use just as a camera, so wifi is turned off as is data roaming and, as far as can tell, any connectivity. But text messages are also coming in on the phone. I have not requested roaming and I don't want to be charged $10 a day to use my phone as a camera. What is going on?
Texting would come through the voice level of the network, so disabling data would not impede any SMS messages from coming through. You would need to activate airplane/flight mode which would disable all your connections, then activate wifi (and bluetooth if needed).
Roam Like Home is not just for data. Although many people do focus on that aspect, as it's the most costly, the service also covers voice, text, and picture messaging. Effectively, you use your phone much like you do at home, for an extra $10/per 24hr period, for a maximum of 10 days per billing cycle.
Hope this helps.