To vpn, or not to vpn

Hi everyone,
I need some help on an issue.

The company I work for has 3 offices. The Asterisk server will be located in one office. The other offices will be connected to it through the internet (no vpn).
At this moment the 3 offices are connected via 1mbit vpn. We are planning to cancel those and upgrade our dsl lines.
The Asterisk server will have an isdn card with an isdn30 line which we will be using to connect and use the PSTN to make calls. SIP would only be used interbranch.

My question is, if we setup asterisk to forward calls to cell phones and one of the branches loses internet connectivity (which happends once a year, mostly during summer) will it still route calls through to cell phones via the isdn line.

Thanks for any help.

If you set up asterisk to do it then you can. You can have asterisk try calling the SIP phone and if it is not able to get to the phone to send the call to the users cell phone.

Thank you, that’s what I needed to know.