Trouble with Tie Lines

Phone exchanges are much more fun if there are more things you can phone. I'll have a load of demo phones connected to the exchange when it's on-site at EMF, but I really want to get it hooked in to the wider phone network.

There are several ways to get a phone number at EMF, you can bring a DECT phone, a wired land-line phone, possibly even a mobile phone... I really want all of those phone networks to be reachable from my installation!

The exchange is equipped with "Tie Lines" which function as junctions between it and the outside world. You can access these numbers from the exchange by dialling an access code. If you've ever worked somewhere with an internal phone system, you'll be familiar with things like "dial 9 for an outside line" - and that's pretty much what these tie-lines were for back when this thing was made.

The trouble is, the PAX is 67 years old (it's seen better days) and so not everything always works first time...