Hi Helen

Do you want to use your phone for voice only? or do you want a data plan also so you can use your phone for the internet?

I only know about iPhones. I bought an international SIM card for voice and data for MARINER and used it in Turkey and Italy. It was very nice to have. I would love to be going on SUMO!

For an international SIM card to work in your phone, your phone has to meet the requirements below. I believe all the newer iphones do.

Your phone has to be factory unlocked. You can learn how to tell if it is here:
HT check if your iPhone is factory unlocked

And your phone has to be a GSM 850 / 900 / 1800 / 1900 compatible international cell phone. To find out if yours is, go here:
Identifying iPhone models

I bought my SIM card from www.ekit.com. Like Mitch mentioned, you can also buy (rent?) phones from them instead of swapping out your SIM card. If you do buy a SIM, be sure to get the correct size. For example, a Nano SIM card for my iPhone 5. The other sizes are Standard and Micro. When what I bought arrived, I thought it was the Micro size (too big), until I realized I needed to pop it out of the surrounding material.

If your phone isn't an iPhone, then, well.... nevermind!