Linker3000 expressed precisely :
> As per the title - has anyone managed to pass an allowed caller ID string
> from a Trixbox extension out via voip.co.uk?
>
> I am playing with a test Trixbox system hosting two phones and we want each
> phone to present a different caller ID to the called party, but the current
> voip.co.uk software seems to ignore this. Even withholding caller ID would be
> OK but this does not happen even if you set it so within your SIP accounts at
> voip.co.uk.
>
> Anyone had more success than me?
>
> Thanks.

Not tried with voip.co.uk, however, thanks to Philippe (for bringing to
my attention), I can now present ANY* of my numbers with Asterisk &
voipcheap.com

*0044870, 0049, 00441, 004479 are four I've set up so far.