If you have an unlimited global data plan on either network, I would urge you to consider just leaving it on. ATT just cancelled its domestic unlimited data plan and probably reconsidering its international options. If you get it on ATT, there are always issues about whether you are a corporate responsibility account, whether your FAN includes it, or whether you can persuade them without a FAN. If you get it, you've got it unless you cancel it. If you cancel it, you will need to revisit that issue and may not be grandfathered if it is every pulled.

I have to imagine Verizon is reconsidering the unlimited situation as well. Rumors are already floating that Verizon may pull the domestic unlimited plans and copy ATT. While I appreciate the $35 a month savings for many months, figure out the cost of data roaming if you don't have the plan. My most recent trip to South Africa involved 850 megs of data on my iPhone. The rack rate for this would be over $12,000. I'm not going to jeopardize this to potentially save a couple of hundred bucks for the months I don't travel.

I could go with prepaid SIMs (which I often use for voice) when I land, but it is usually a day or two before I get those SIMs, the data plans may not be great deals, and there are frequently Government mandated registration requirements with the SIM.

I frequently can make VOIP calls over 3g and that is a nice savings. I can use GVMobile to trigger callback calls to my roaming SIM reducing my cost for outbound calls to the US to under 20 cents a minute in many countries.

If I were you, I'd leave my plan on 24/7 unless you are really hurting for money.