New in VOIP, Help!

I am new in Asterisk and VOIP. I want to setup a Linux machine with Asterisk and use VOIP phones between multiple branch offices. Could someone suggest me the components I require. What additional things are required to connect my asterisk system with PABX to route calls to PSTN network?

Highly appreciate if someone help me on it.

What system are you goint go connect it to and\or how are you planning on connecting Asterisk to the PSTN (T1\E1, analog line etc)? How namy lines are you planning on?

Dear Swaterhouse,
I’m new in asterisk. So, I need your suggetion, how to do everything?

Dear Walter,
I would prefer option 2. Could you help me explaining about the technicalities of this option.

Thanks again!!