I also get my credit balance displayed on screen in the way that Lie-in-King does. However, if you'd rather listen to it, dial (or should that be 'key in'?) 1345. Both services are free of charge.
Creditline: 2345 (Free)
Helpline: 191 (25p per call, unless it's gone up since I bought my phone!)
If you forget your number: *#100# (Free)
Voicemail: 121 (standard call rates)
Emergency services: 112 [or 999]. (Free)
Fault reporting: 151 (Free)
To switch on 'Immediate divert' (so that you calls go straight to Voicemail, with you receiving a text alert): 1212 (Free)
To switch that facility off: 1213 (Free)
Switch Voicemail off: 1210 (Free)
Switch Voicemail on: 1211 (Free)
Chris