Good answers from the regular contributors here.
I am using the exact setup that you are asking for, I bought 2x110 and place one in the office and the other at home, both connected to PSTN lines and no VOIP services. Here are some tips that I learned the hard way.
1) Use ObiTalk to register both Obi110 or signup two Obitalk account, dedicated to each Obi110 device. The Obitalk is another service besides the VOIP/PSTN/auto attendent. In the beginning I was confused which is which. Then use the Obitalk Expert configurator to change the settings of the Obi110, instead of using the build - in web browser in the device. The advantage is remote configuration and ensuring that they are online.
2) By default, once you power on, both Obi110 already is setup to put phone calls through the Line port, so if you you plug in a normal analog phone to use ObiA (with dialplans or autoattendant) to call ObiB number (the 9 digits phone number starting with 290 behind the device), the phone on the ObiB will ring and the conversation is through the internet (ie no cost).
3) If you want to implement your idea of your friend Call Obi A number which automatically send the ring and call to ObiB, you can set the call forward settings. But this could mean that ALL calls goes to ObiB, making ObiA redundant. This is useful you are trying to lower international calling cost by putting ObiA on home ground and sending ObiB to some other countries....The other way is as others have mentioned, you need to setup the auto attendant to redirect your caller to obi B when they dial the ObiA number(s)
