Brv let me explain this in detail to U ..
1. For mobile credit only workable sollution is carded credit / vouchers which adding the price of dumps .. max credit value of 50 gbp and considering instore carding risks ...well also one has to consider that you are giving money back in 3 weeks and just 50 % ...
2. Now any one who is in Voip game know and will tell U a good voip server can setup around 500 - 1000 connections simultneously ... so an average server can load around 10 k 15 k mins a day ... may be your premium number company wont have charge back but the voip company will block your numbers on server with in 24 - 48 hrs max. So if one finds a server that is open rule of game is to squeeze as much as possible in shortest time .. and to kill a server for just 100 200 mins.Its just like getting a bank login with 10 k in it and then killing the login for a 200 gbp faster payment ... I hope you understand ..
Personally i will reccomend to you for your setup try to get some skype accnts and see if it works on them .. may be it does and then you can have your own system running ... u can get skype accnts for like 30 % of value and u can make 70 % on them ..
hope that explains my concerns
best of luck !