IP Phones, how make calls?

hello,
i am very new to IP phone so a lot of confusions.would like to put this senario for example, I have office (A) having a router with public address and one IP phone, I have another branch of my office say office (B) there is one more router with public IP and another IP phone.
i want to make call from (A) to (B) with out any call charges how to do that,how to dial to other IP phone at other branch.

please let me know steps how to accomplish this task.

what IP phones to use because there is a lot of variety.

thank you.....

try using one of the freeware VOIP software
http://bestofrest.blogspot.com/search/la...

I presume this IP phone comes with an IP phone service, so that you can use it to call anywhere in the country or world? And I presume the other IP phone comes with a similar service? So both phones should have phone numbers. Just dial the phone number of phone B from phone A.

There ARE systems which will allow you to make a call within a single LAN / WAN environment without ever going onto the public phone system, but these are large industrial systems (I know that Cisco and Motorola (formerly Symbol) both offer such systems). In this system, your phones are all assigned extensions within the plant's PBX. If you dial an extension that is another IP phone, the call just routes through the LAN and never goes through the PBX. If you dial a normal non-IP phone, the LAN routes the call to the PBX which routes it to the destination extension.

From what you wrote, it doesn't sound like you have such a sophisticated system, but rather one of the new IP phones which just takes advantage of your own local wireless router. With this setup, you can NOT make a purely INTERNET based call. Your call from your office will be routed to the VoIP providers system, then switched onto the POTS public phone system, then routed BACK to the VoIP provider for Phone B, and then over the internet to the final phone. Complicated, no??

BUT, since you've already paid a fixed montly fee for the VoIP service, it shouldn't cost you anything to actually make this call.