You know that’s two completely separate things, right?
Configuring the phones as extensions is a well-understood set of changes - the OSS EPM (theoretically) should be able to handle that. If it doesn’t, submit a ticket so that people working on OSS EPM can get your issues squared away.
The trunking is fairly simple. Set up your trunks so that they use your outbound trunk (a SIP connection to an TISP would by my suggestion) and set the outbound route to talk to the trunk.
I usually recommend VOIP Innovations and Alcazar. Both are pre-paid and cheap (less than a penny a minute for outbound). If you want the FXOs to be your outbound trunks, you should be able to so that relatively simply. now that they are staying connected.
My GXP2130 phones are already configured as extensions. That’s how I tested the outbound dialing.
The wiki page on configuring HT-503s talks about trunking. Now that I think I’ve solved the grief of the first step, I’ll go back and follow those next steps. My point about the 2130s was more a provisioning step: I need to figure out how to setup a graphical button to select and connect to one of those trunks once I set them up.
Yes, I am aware of the wild and wonderful world of VOIP getting all this setup has made available to me. For now I just need to get our two POTS lines configured. Hence my travails with the HT-503s. I even see the module for Google Voice. I’ve had a GV number for years. A future project. After voice mail. After I get the call boxes on the property connected to the FXS ports on the HT-503s, etc, etc.
Posting this months after my last post. I realize I never shared that I did get my HT-503s working. I updated the wiki page linked above with what I learned: