The ideal process is the user would put his phone number into the web app, he would receive a text message, "text back <some PIN> to pay $X," and then payment would send a message to the web app server, maybe GETing something like Y.com/payment?from=5555555&secret_key=ZZZZZZZ<p>I'd like to get recommendations on who to use, and it's be great to know if anyone has used SMS payments in their own projects, and how it worked out.