I really don’t care about transport ie RC or others(most are hipaa compliant). API integration will be the same or similar so real issue is cost. Also attention needs to be paid to how it gets used in OpenEMR ie workflow, if you plan to tightly integrate to OpenEMR.
Maybe adding the API to my existing front end will allow users a choice of several different fax/sms vendors which is always nice. Similar to credit card gateway. Who is this API with? Are you planning to put in OpenEMR this new API?