As often is the case with these big firms who have lots of customers who only make them a tiny amount each they put a huge amount of work into making sure things work 99.9% of the time, but don’t really care an awful much about the .1% of people who have a problem, well they do care, but it’s not worth investing a huge amount into it – it’s just financially not – hence the terrible call centres, and slow responses.
I don’t suspect any of the other providers are any better, it’s just a case of rolling the dice on providers and hoping you’re not one of the 0.1%.
It’s worth noting that most businesses who use mobiles use a broker – it costs more but they deal with all the customer service crap, usually through dedicated broker helpdesks.