SMS test with airlink RV50

Hi
I need to confirm my SMS gateway is working. I have set up a test alarm and pipeline that only sends the acknowledge code in the message, the idea was that the alarm would acknowledge itself to confirm SMS working. I have tried sending this back to itself and also tried sending the SMS to external router that auto forwarded the message back. I can see the correct massage returned in the Airlink but alarm dose not acknowledge. It appears that only SMS replies will acknowledge not forwards.
Any ideas on how to make this work or other options for SMS testing.