Does anyone out there know the dial code to turn on an off the CLI (call line identifier) on a Telefonica land line 'phone?

Do you mean to withhold your number if you're calling someone? If so, it's 067. Sorry if that's not what you meant!

067 hash 31 hash will block out your number when you dial out. The hash 31 hash I have no idea I have it written next to the 067.

#31# is to withhold your number when calling from a mobile.
From a Telefonica landline, as I said above, it's 067.

You will have to phone Telefonica to get them to do it at their end, it`s one of their extra little hidden costs. ;-))

Have been looking for the number for ages, went right thru telefonica manual but could not find it, many thanks for this reply.

Thanks for everyones help, looks like I'll have to call 1004 to get them to put it back on, it's for a friend of mine and the CLI is not going through anymore, so some people won't answer the 'phone when they see "private"

I think it costs 50 cents / month

50 centimos per month is to subscribe to CLI when receiving calls. When you make calls your ID should show up automatically unless you prefix the number with 067 as already stated. I don't think you can turn it on and off per se.