Site with private files access based on roles

Hi. My situation is this: I'm building a site with premium content. It would be accessible by only certain roles and you would get a promotion to that specific role by sending a text message to the operator number, which would then send a http/php request through 3rd party SMS gateway to our server and activate the user.

The role should automatically expire after six months and return to the basic registered role.

I need help selecting methods and modules to do this. Please add good suggestions if you know any. I have been looking for the Private upload ( http://drupal.org/project/private_upload ) and Contend Access ( http://drupal.org/project/content_access ) modules for controlling the private videos and nodes.

The expiring roles give me a lot of headache. I have found only one solution so far, the Account Expiry module ( http://drupal.org/project/account_expiry ) The abovementioned module doesn't really fit my needs since it makes the account into inactive instead of doing a fallback to regular member. Also, I don't know the hook to make the http request automatically promote to the premium role.

I have also heard that Ubercart ( http://drupal.org/project/ubercart ) has some kind of an method to buy premium roles but it seems just a bit overkill for my purpose. And also, I don't use the paypal payment option etc. because of the SMS gateway method of ordering.

I know SMS Gateway module exists ( http://drupal.org/project/smsgateway ) but I really don't know if I should use it.

I'm getting some helping hands soon but meanwhile I need to know which route I should go with this project. Any help is much appreciated! :)