I pay £29.99 per month for my landline and broadband - with BT - this includes and payment of £5 monthly to give me all calls to landlines in UK and mobiles without any extra charge. My mobile (which I always buy outright) is with 02.
Originally, I paid £10 a month and never ever came close to using all the data on it. Just over a year ago, I had a problem with my phone, and took it into an 02 shop and they asked me how I used it -and then suggested they change my contract to £7 per month!
The only time I ever came close to using all my data was in the first week after I moved home, and was waiting for BT to install my landline and broadband, and was having to make loads of calls, etc regarding my new home.
Think we have to think about checking these sort of arrangements annually, in the same way as we do our other utility bills, and insurances.
PS: Both BT and 02 have slightly increased these charges, by pennies, due to cost of living index - I did query this with BT as I have a two year fixed contract, and was told that they are permitted to pass these increased on to to their customers.