You can call into the Comrex units in BBC Radio's MCR1 (formerly LCR) using their BBC SIP address from ipDTL's dialpad, or a sip.audio enabled client. An internal booking must be made first.
The BBC can also connect to sip.audio or ipDTL users by dialling their SIP address.
Should the above method fail, ipDTL and sip.audio users can enable 'Receive 3rd Party SIP' in their account settings and use the following workaround. These instructions are for the producer to pass onto the BBC's Network Bookings department...