1) When scrolling to compose "new" email, go to compose PIN or Send PIN.
2) No as long as you have GPRS server and in a country/location that has GPRS.
3) They are sent via GPRS so the data provider's gateway is used on both user's BB.
4) Once a BB is 'Blackberry Data provisioned', yes.
Mike. Great questions. I will post a more detailed PIN FAQ to this soon, so check back soon.
Hope that helped a bit.