Text subscription sofrware

charity subscription system for a gift leasing
i need In order to achieve what i want to do is a system setup which manages the subscriptions by text. which would work like this: send a text set up the value of the gift ie £10 then a weekly subscription of 10% minim £1 to phone number until the gift is passed onto to a new subcription or the £10 have been paid in full. the subscription will be a charity gift so it would need gift aid details