hard coded numbers

In my usage scenario random members want to text each other via a site directory. That means both the “from” and “to” numbers cannot be hardcoded. Your description asserts messages can be sent to *any* number. That’s good – that solves half of the problem. What about the “from” number though? Does that need to be hard coded so that the site acts as middleman? The use case is a member selecting another member as a message recipient. When the target member receives the message will he/she be able to directly respond to the sending member, i.e. as in a normal direct text message exchange? What I don’t want is the recipient responding to the site or needing to initiate a new text session in order to directly contact the sender – that would be awkward and ungainly.