Just issue ATX0D on one modem and ATA on the other. Bingo bango: One modem thinks it's initiating a call (without concern about the lack of dialtone), and the other thinks it is answering a call.
But yeah, simulators are fun. A person I used to call "boss" used one with a dry pair of copper that ran all the way across town for his internet connection for a couple of years.
(His shop had space that was used by a local dialup ISP for a POP. In exchange for the space and the electricity, his shop got free internet over a T1 in the days before we had DSL or DOCSIS. It was a great trade for both parties and I felt giddy downloading things at work at >1.5 Mbps instead of ~0.0336 Mbps.
In an effort to save some money on a dedicated phone line and ISP bill at home, he ordered a cheap circuit from the phone company that they billed as an "alarm circuit" -- it was about $20 per month.
One modem was his at house behaving mostly-normally along with the simulator, and another was at the shop connected to our all-singing, all-dancing 486DX4 Linux box. It was stable and cheap and somewhat ridiculous.)