Call to PSTN from Asterisk

Im new in asterisk and i want to create dial plan for calling PSTN the detail is as under.

Asterisk : Asterisk-1.4.2
Telephony Card: IVR Card- 4 port digium

I have installed asterisk and along with my telephony card both are working well and Iam not able to call PC to PC (SIP). But my problem is that I cannot call on PSTN.

I want know that how can I configure trunk(Dial plan) in above scenario.

You response is really encouraged me and hoping for your quick response.

If everything is setup and working properly you can use something like this:

exten 100 => Dial(zap/1/${TEL_NUMBER})

You may want to change exten 100 with pattern matching (for example I use _0XXXXXXXXX for a cell operator in my country). 1 in Zap/1/… is the channel - if you’ve groups configured set them instead. (Zap/g1 for example).
Good luck!