You can use our pool of Shared Numbers when using HTTP API.
The parameter you need to include with your HTTP API request is 'api=1'.
Please note if you're sending from our Shared Numbers, you do not have to set the 'from' parameter.
For more information, see our HTTP API Documentation.
If you would like a copy of the SMS replies emailed to the account email address, you can add the parameter 'apireply=1'.
Note: Shared Numbers can only receive replies within 48 hours after the outgoing SMS is sent.
Note: For further details on Shared Numbers and other sender ID options, see here.