I would suggest you contact RAIN at their customer support number and ask the question. I also use such a router and it is a valid question for many South Africans.
1. Your reply is very valid, but in most cases RAIN utilizes other SP's towers to connect to.
2. With the current client market of RAIN, I would think that RAIN would actually provide such info to protect their own routers and provide a doable solution for a 4hour entry level UPS within a R1,500...