Whats the most inexpensive cellular service to call USA & Canada in PK

Assalamu alaikum

I wanted to buy a SIM card to use while I'm in Pakistan to call my family in the United States and Canada.

So I was wondering what cellular service to get?

I hear "PrePay" is much more inexpensive and convenient in Pakistan...

So what should I get...

Mobilink Jazz

Warid Zem

Telenor

Ufone

Zong

Also I just got a Sprint EVO 4G, Which is a CDMA phone, Is there any CDMA service provider in Pakistan???

I appreciate your time and input...

Thanking in advance...

well yes prepay is inexpensive here...

i suggest Ufone

call charges to mobile & fixed line for both USA & Canada : Rs. 2.2 per minute.....

Would that include all tax???

I've read somewhere in Pakistan they have 29% tax on cell phone usage..

well they will be increasing taxes as per world bank and imf directives..so tax rates will go up and up =(