Three have always been, to me anyway, like that girl in the nursery rhyme;
When they're good, they're really, really, good,
And when they're bad, they're horrid.
Cheap enough, and reliable enough, for me though
I know other people that are happy with them, but when something network related goes wrong, customer services can be rubbish.
That said, in all the years that I have been with my provider, I have had numerous odd things happen that took multiple calls to resolve.
The first was misrouted voicemails. I would press the voicemail shortcut key (1) and then have loads of messages from northern people talking about the houses that they just looked at. When I first rang customer support they warned me that hacking other people's voicemail boxes was a crime... I resorted to ringing my own number and leaving a voice message, in it I explained that our voicemail boxes had been switched, I then left my number. The guy, a northern estate agent rang me back and mentioned that he thought it odd that he had Londonders asking about prices to repaint their homes. It took about 7 calls to customer support but on the last call, the tech support realised that my phantom mail box number had been switched with the estate agent's.
The next was being charged twice for every SMS I sent. I would send one, the recipient would receive two, I would be charged for two. Again, many calls to customer services, but it got sorted because one identified it as database corruption on their system.
My concern with a virtual network is that the staff will not be willing to escalate the problem with the likes of EE.
Yeah, fair enough, how many people have those kind of problems? Through no fault of mine, I have. I may need to make many phone calls and insist that things are escalated but I am more confident that the network owner has a better chance of finding the solution than a virtual network.