[GadgetKen]

You may want to consider getting 2 international callback sims. Most have long expiration dates which can be extended by making a brief call or sending an sms text message a couple of times a year, and many can be easily refilled over the web. The United Mobile brand has been around for many years and use Mobilekom Liechtenstein as the backbone carrier. CelTrek I think uses Orange-Israel as the backbone carrier and is a newer operation, but has better rates in some countries (and worse in others) and lets you choose an incoming number in the US, UK or France.

That way if
1) there's a technical glitch with one card that can't be solved by redialing or selection of local carrier,
2) one callback sim offers a better rate than the other in the country your in, or
3) one sim lets you roam on a carrier with a stronger signal where you are trying to make a call from,

you can just swap sim cards.