Prepaid mobile sim card to be used in Toronto and New York

[dyaan]

Hi Guys,
By the grace of almighty Allah (swt), I will be landing in Toronto YYZ on 11th May 2013.
While I am planning and arranging stuff for my landing, I was wondering if anyone could help me the following:

PREPAID Mobile PHONE SIM CARD:
1. What will be the cheapest Prepaid Sim card that I can buy for my blackberry 9900 (unlocked).
2. Since it’s my first landing and I would like to call back home asap , can I buy the prepaid Sim card @ Airport itself.
3. I will be visiting New York for @ weeks immediately after landing in Toronto, therefore I am looking for a Prepaid Sim card that will work well and cheap in USA as well. Please suggest.
4. If I run out of mobile phone credit in USA , is there a way that I can top up my phone with talk time their ?


Thank You,

Dyaan