How to do this? FreePBX connected to foreign non-FreePBX

I have FreePBX running at home with multiple extensions. I’ve just joined a company that uses SIP and has PBX type unknown. I’ve connected to the office PBX, treating it as a trunk for FreePBX. To the office PBX, my connection looks like an extension.

This works in that I can dial out and receive calls. However, I also need to be able to dial internal extension numbers at the office. This doesn’t work, because FreePBX thinks I’m calling one of my internal extensions.

Any suggestions how to get around this?

You would want to configure an “outbound route” on your FreePBX system to connect via that trunk using that extensions dial patterns. You can get a general idea of how that would work from this wiki article.