We need a backend to a current program.
There's 3 plans, A,B and C. You can have a look at it here: [url removed, login to view]
If you browse through the options, it is pretty clear what happens when a users signs up for an account. He/she could buy extra credits/servers to get more notifications, this should be tracked in their account details and dealt with accordingly. A users pays by paypal (recurring), we have a script ready for that which might be good enough. It might need some tweaking, not sure.
This also includes implementing the gateway that sends the message (which is easy).
Please let me know if you can handle this, what timeframe and at what cost.
If you're the right person, we have more projects and we'd like to use you on a regular basis.