conference between a sip softphone and a POTS line

Hi, I'm trying to do the following, I'd like to know it's possible, and if it is, if anyone could throw in some suggestions on how to accomplish this I would be grateful -

I'd like trixbox to call my cellphone using a POTS line which I'll supply into the system using a Cisco SPA3102 analog adapter (it has an FXO port).

After the call gets answered, I'd like trixbox dial an extension.
Then, I'd like to set up a conference between the two inside trixbox.

All that has to be done automatically.

Does this scenario requires a special modification? Is it possible at all?

Thanks beforehand.
Max.