If you want to call Pakistan from outside world, we always recommend to choose cheap calls to Pakistan plans for long term but If you are looking around "free calls to Pakistan" that is almost impossible, there is nothing really for free. But yes there are plenty of VoIP termination competitors which can help. However here is some info from "evongetz" that may help you to try some cheapest way to call Pakistan through SIP.
The Session Initiation Protocol (SIP) is a signaling protocol used for establishing sessions in an IP network. A session could be a simple two-way telephone call or it could be a collaborative multi-media conference session. The following Carriers give SIP accounts, Send someone to their office and get an account, and configure it in your switch as a route, and start sending traffic. We will not go in more technical details to avoid confusions however if you are regular office or home caller to Pakistan then you should definitely look for the permanent solution to stay connected on daily basis.
Therefore, we can give you some Pakistan VoIP providers info who maybe can help you to provide you desired solution. We can't give you exact package detail that what they can offer as PTA policies are involed which sometime doesn't let these provider to show up their actual calling plans. Hope you got the point.But still the typical cost of this will be 1 cent a min ( 60 paisa per min to land line) to Pakistan. The following companies give SIP accounts, and you can buy them, and configure them in your system.
Hazara Telecom www.hccnp.net.pk
Soon Link.net, and PTCL. Wi-Tribe will also a good SIP player in Pakistan's voip market, currently Wi-Tribe launched Broadband Wireless internet. their slogon is "Online with no line"
Updated: The above PTCL comment is no more valid because PTCL has started providing VoIP services to the customers.
Wateen and Burraq: Get a Wimax box, and get a local phone line with it. Then email to Wateen and ask them the sip password for it. They will send you the SIP configuration, If they dont, search on google, on how to get out the sip password out of wateen box, u will find a LOT of links. Configure this sip account in your switch as your route to Pakistan and enjoy the 60 Paisa a min or 1 cent a min service from them. Here is also a direct person who can help: Hi! Terminate VOIP traffic on Wateen @ $0.02 Per Min, We will help you generate revenue in the growing VOIP market for Pakistan. You will just send it to our "HighlyIntelligent Routing Server" and it will be delivered to wateen. Our device is the only one in market which have the ability to terminate traffic on wateen. Thanks Regards, Robert Hill VOIP Wateen Expert! Contact US