W70B - Associate Dialed Number with SIP Account

[karibi]

I have a number of SIP accounts, for example one for the UK, one for South Africa etc.

What I would like to achieve is:

(a) If the number begins with the country code for the UK use the UK SIP account.
(b) If the number begins with the country code for the South Africa use the South African SIP account.

I don't believe the dial plan offers this capability. However this seems a fairly basic requirement, so am I missing something?

Thanks