A couple of questions 1. How much does it cost? is it worth it? 2. Does it support buycraft? 3. Does it support custom store plugins? 4. Where does the money go? Thanks!
you need a payment provider that supports that. stuff like paymentwall support multiple providers, including mobile: https://www.paymentwall.com/en/payment-methods/ http://www.mobiamo.com/ is a big mobile provider. generally, if you need buycraft, check here http://help.buycraft.net/category/5-payment-gateways money often goes to a virtual wallet where you can cash it out or it goes directly to your bank. just note that most providers require stuff like tax ids from you.
Building your own system will take much time and recuirring payments monthly based. I recommend that you stick to @MiniDigger's idea because its the easiest i can think of. As much as i know BuyCraft doesn't support SMS donations as a method but it supports other methods such as paymentwall that do use SMS payments.