We already have external module if you will that we are using for one of our 12all distributions.

The process is fairly simple. You basically need number discovery via a HLR lookup provider. Google it, you will find dozens of providers.

We simply added a little magic into our forms integration that allows two accounts to be created for our subscribers. One for email, one for SMS if they choose to use it. If they add SMS we conduct network discovery via HTTP API and Web SMS interface to discover their home network and simple auto insert the address extension binding it to their phone number. If the HRL fails, we ask them what network they're on on a select list.

The downside is there are two accounts for each subscriber but at the end of the day who cares right? So far it is working REALLY well for us, we have a few homeowner associations who want to send SMS campaigns alongside their email campaigns.

Naturally I would like to see 12all inherently create this into 12all but last time I checked they did not have any immediate future plans to do so which is why we wrote our own.

Love that my idea worked its way into the product. WOOT!