I'm interested in an ATA with two internal extension ports and one
(analogue) PSTN connection. I'd like one of the internal ports always to
default to the PSTN line, but allow routing via at least one SIP provider
given some particular key sequence prefix (e.g. #001*, or whatever). The
other should default to one of the SIP providers, but allow routing via
either PSTN or any of the other SIP provders given some particular key
sequence prefix.

Pricing would ideally be towards the lower end of the market but
definitely sub-£100.

Any suggestions, please?

Many thanks,
Chris