SMS sending application that connects with my website

I run a SMS website which registered users send SMS from it. They must purchase credits in order to send messages. The application must: 1) let my customers send SMS messages without having to log on to my website. 2) log all messages onto my website for admins to view 3) log all messages on website for users to view 4) deduct the appropriate amount of credit from the user's account when they send a message (price is liable to change) 5) display the amount of credits the user has remaining. 6) have the same functionality as when my website is used to send a message (user can define their own sender ID if they have agreed to separate terms and conditions - if they have not agreed then they can only send from their own number (all this data is stored in my site's databases already) 7) be able to tell if a user has the required credentials to use the software - i want to be able to decide to can use it and who cant (for example I may want to have the use of the software as an extra subscription option) This list of features is not final, but it gives a good idea of what I am looking for. Other features may be necessary as well, but it will be nothing beyond what would be expected of a basic bit of software like this. My website runs on windows server with MS Access databases