By the way, I found some old PC based software which seems to configure a bridge between 2 SIP calls on a PC running back at your home. It is meant for bridging an incoming call on one DID to an outbound SIP call (any provider), but it can also be configured for callback. From the user guide, it seems to be very easy to use and set up. I know this can all be done if you are Asterisk savvy but for an amateur like me this seems pretty perfect. Unfortunately, the software costs $29. However there is a 15 day evaluation period. I have not tried it yet, as I may save my evaluation period so that it occurs during my holiday when I will need to make use of the callback. Knowing my luck, the evaluation version will not allow callback.
The software is called dialbridge and it can be found here:
VONaLink - DialBridge for Windows
Info on the callback method can be read here:
VONaLink DialBridge for Windows User Guide