Send SMS from desktop app in Mac OS

We need an app that allows users to send SMS through an account with credit hired with us. The app core is HTTP because the app makes requests to our API via POST and receives response with all data needed in a XML document. App shows information contained in their account, as book address (name and phone number), delivery lists, SMS sent list... App must allow import contact data from file. App must be localized in Spanish, English and some more, but we provide everything you need translated. The users must login to the application. The security in calls is through HTTPS. We have developed this app for Windows, and it will be useful to know the limitations. We provide all the commands to call, the test user, and screenshots about design...