I suppose, in theory, coverage will be better abroad as T-Mobile have agreements with 5 telco's in The Netherlands whereas in the UK I can only use T-Mobile. I'll give it a go anyway, off to Holland tomorrow for a couple days.
So in reality, Mobile Co's in this country should create treaties or contracts to carry ALL network traffic irregardless of which network your phone is on. This should be forced by the GOV.T: at the end of the day people in dire need of emergency should have access to AT LEAST ONE NETWORK SIGNAL.
Don't they already do that though? It's been a while since I've seen it but my old phone used to switch to "emergency calls only" mode which presumably is free 999 calls via another network.
The trouble with that is controlling prices paid by the consumer - if you are using a T-Mobile handset, but make a call using the Vodafone network, both of them will levy a charge for that call, in just the same way than international roaming works.
I can agree with it being useful for 999 calls, but anything else I guess will be problematic. If we're network sharing mobile networks will be less interested in improving their own network as their users can use the others.
Excellent service in Holland. Great network coverage. I used T-Mobile NL most while I was there - nice touch getting a text from T-Mobile UK thanking me for connecting to their sister firm with a number to call customer services back in the UK.