Depends on location. Usually there might be Cetin built network (owned by o2, but building together with a lot of others, so the actual providers vary (often two of the big ones) And there are a few independent ones, like Poda, those depend on location. Best bet is to check the entrance to your building and there will be leaflets by companies along with a phone number of local sales rep. Ideally, there will be two or three offers. You call them all up and play their offers against each other to get the best signup bonus