You can have prospects send an SMS to your ONTRAPORT SMS number to opt in. The SMS message must have all the data on one line with elements separated by a space (and not on a separate line).
The accepted formats are:
1. Email address. Example: email@example.com
2. Firstname Email. Example: Bob firstname.lastname@example.org
3. Firstname Lastname Email. Example: Bob Smith email@example.com
see details at http://support.ontraport.com/entries/...
You can also have an opt in form with the SMS number field for the contacts to opt in using the form.