Moved over to Three last month. The first bill should have been £18 (one plan sim only) but I've been charged a few quid more. I don't use any services outside my allowance (e.g no premium rate numbers, MMS, TV voting text numbers etc). The only thing I can think of is that they're charging me for voicemail which I don't think is right.

Unless I'm going mad I can't actually find a breakdown of services used, like Vodafone online used to offer me (list of who I phoned / sms in the month). Can anyone help?

Like with every network, your first bill is always higher because they bill you for a pro rata allowance.

If my calculations are correct then your first bill should be £21 or £21.60. right? Same happened to me when i got my contracts out.

You can view bills and stuff on the my 3 account page -
https://www.three.co.uk/My3Account/Login

You're right I didnt consider that when I saw the charges. It should all even out next month then.

I was surprised they didn't express that to you at any point, I must have been told about 10 times in the shop

EE and T-Mobile don't pro-rate the first bill to avoid this kind of thing

They also send a text message to that effect as well - both indicating when the bill is prepared and why it might be higher than expected - with a link to a web page that describes in detail.