Existing Switchboard

Hello out there, I would really appreciate some help…

I have Asterisk set up and it works great!!! Thanks to all developers out there. The problem I have is that I would like the digital receptionist to forward certain calls to a trunk which goes out into our existing switchboard which is not a pbx. In other words, if I call into the digital receptionist, I can dial 1, wait for the dial tone of our switchboard, and then continue dialing the extention. I would like to have Asterisk do this outomatically. Is this possible? Could I set it up that as soon as someone dials a number that has three numbers and starts with one that asterisk forwards it into trunk number two but it would put a pause in after the first one to wait for the dial tone. Are there any suggestions.