I copied this off another website. Anyone with BT who uses call divert might save a little bit with this knowledge. As it's my most commonly dialled number (my own mobile that is) I also have a best friend discount on it.
QUOTE
Sneakily get BT’s £1.50/mth Mobile Call Saver for free. ALL mobile calls 7.5p/min
BT's £1.50/mth mobile call saver add-on slashes the cost of daytime calls to mobiles by 40%, from 12.5p/min to 7.5p/m (plus 7p connection for both). New Promo: Sign up before 31 Dec, to any of its calling plans and it's free indefinitely, provided you keep renewing the 12 mth contract. This includes BT's basic £10.50/mth line rental unlimited weekend plan. Got BT? Get it free: The sneaky bit is, even if you’re already contracted to BT, call up/go to your online account and ask to start a NEW 12 month contract and you get it. 6p Mobile Calls: BT is beatable though, open a 18185 account and dial its prefix number and it's 6p/min plus 5p connection fee.
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I have tried diverting these calls via an override service (such as the 18185 service mentioned) but diverted calls can't be routed that way. It only works if you dial the number manually. However, I do get a lot of calls diverted to my mobile - especially since I started advertising more - so I will probably start a fresh 12 months with BT (unless I find a better deal elsewhere).
Hope this info might save some people a few pounds.