OK Petkow you are going to tax my brain here, I had it explained to me over a beer in Palma last year!
We had a technical email from Gymsim about it too but I cant find it now.
The numbers come from the Isle of Man - due to having a GSM mobile licence there.
The calls are routed by British Telecom - To make call quality tip top
The other stuff like the ability to roam, roaming agreements, connecting calls and signaling etc is all done by TIM.
It was explained that in roaming you have to appear big or you have issues with other networks not prioritising you when you roam on their networks. It gets bad for those crew in the touristy areas in the Med during the summer as you often find you just have constant problems when the base stations all getting loaded with traffic, (but in the winter you dont have a problem). In Monaco during the Grand Prix it's almost impossible for anyone to use their phone. I have had problems with both incoming and outgoing calls when using my old Callkey and United Mobile Sim cards due to deprioritising, So then you always have to manually hunt around looking for networks that are working OK which can be a pain. So with TIM being one of the big players (one of the big 5 networks?) means you appear bigger then you really are so you get prioritising as well as a reliable network.
I should find that technical email, it was full of interesting goodies about roaming, makes you realise how hard it is, its a bloody miracle the whole roaming thing can work at all. They had a shocking statistic that indicated roaming in Europe runs at about 80% success, and it drops to 40% when you are in third world countries. I was in St Martin and Antigua this year and both had problems with networks that stopped working completely for days at a time! (The power station in St Martin blew up which couldn't have helped
There was also something about a ship dropping an anchor on an underwater telecommunication cable which cut off parts of the middle east for a few weeks, it happened twice last year! Lol I loved that one.
Hey Dg7feq, I didnt ask Sonia yet for the info, will shoot an email just now