Only the AT&T iPad will work outside the USA. The Verizon model will only work in the US and a very few other countries. Many members have successfully purchased iPads in the USA and have had no trouble getting them to work with non-AT&T SIM cards, although there has been a discussion as to whether the iPad needs to have its 3G activated initially in the US. Most Members choose this safe route and activate their iPads in the US. We have a mix of other Members who have not - some have reported difficulties in activating their iPads when they got home (having not done so in the US) while others seem to have no problems at all.
Tim