Re: @ Mephistro (@ Technical Ben)
I'm in Spain, and we have a few sim-free telcos with nice offers as well, although their market share is not too big yet. Regarding the costs of renting the big telcos' networks, there is a legal cap on what said networks can charge, based -if I remember it correctly- in a percentage of what big telcos charge to customers -for the use of the network alone, without including other products or services.
IMHO the SIM-free telcos can earn some serious €€€ with the remainder of that percentage, due to their lack of overheads.
On a side note, I was under the impression that most Western countries had similar laws regarding landline and mobile telephony, so if any fellow commentards can confirm or deny this assumption of mine, I'll be grateful.