We have a similar product which uses an https gateway and a Delphi front end.
Out program haves a similiar Outlook interface in which you have:
1. Folders (incomming, outgoing, sent and recycle bin).
2. Contacts (just name, phone and e-mail address).
3. You can define your own groups and one contact can belong to more than one group.
4. You can send a SMS to more than one contact and/or group.
5. You can set "recurring" messages. The model is similar to recurring task on Outlook: daily, weekly, montly, each first day of month, last day, etc.
We can:
1. Change our product to talk with your http gateway.
2. Translate to your desired language. If isn't english you must provide us with the correct string values.
I wish I could include here our web site in which you can download the application but it is against the Get Freelancer service terms.
Regards.