Generally call centres have got a lot better for less waiting time in the last few years, whenever I have to ring the ones I deal with (banks / car insurance / energy suppliers, car finance) I usually get put through within the space of a minute or so - during the day that is. If it's evening then it may be up to 5 minutes in my case.
I'll never forget back in 2006 when I had to ring what was Orange on a weekend when my mobile SIM wouldn't work properly on / off - it took nearly two hours to get through to someone. Luckily at the time Orange to Orange calls were free and the operator had no idea how long I had been waiting until she asked me & was very apologetic, and it paid off as I got 50% off my next bill.
Though whenever I've tried the call back feature a couple of times with different companies, it usually takes half of the day for them to return my call.
Liam.