Connect my ISP SIP provider to my Asterisk System

Hi everbody

This is what I got right now:

Asterisk 1.2 up and running, with a few extensions. SIP calls can be made between extensions, using SJPhone.

I have 2 SIP lines from my ISP provide, who also provides SIP service. Let’s call them 555-0001 and 555-0002. Those lines are connected to the standard copper lines from my town. So calls can be made between softphones and traditional phones.

What I want?

People can dial 555-0001 and 555-0002, my SIP provider forward those calls to my Asterisk system, which then plays something like “Welcome to blablabla enterprises, please press 1 to blabla, 2 to blablalba, etc…”. After that, forward the incoming call to the established extensions.

Is that possible? It would be great to have an example!

Thanks in advance.