By “best” you mean cheapest, right? If so, then do your current phones use sim card (I’m pretty sure T-mob does)? Are they locked into contracts, or are contracts fulfilled and phones unlocked from Sprint and T-mob?

If both phones use sim chip, and both are unlocked, then you can just purchase pre-paid sims on arrival. To get the cheapest rate, you will need to buy a new sim in each country. Supermarkets, corner shops, some post offices have them — they’re easy to find. When you leave that country, you will then be roaming, and any remaining credit on that sim will get used up much more quickly. You might be able to make calls for 10c/minute within the country, but cross a border and it’s easily 5x that much (EU capped roaming charges around that amount this year, IIRC).

If you’ll have a laptop or if either phone is wifi capable, then you could just use Skype.* To extend wifi coverage, you could pay $8 for a month of Boingo, but even Boingo isn’t everywhere.

Before skype, boingo, wifi, and laptops, people used to use these things called “calling cards” at “pay phones.” Pay phones are harder and harder to find, but if you do, you can always purchase a 5 or 10 Euro card, call the prescribed numbers and scratch-off passcode (or however they work these days), and whoomp — there it is.

*If you’re going to try skype from your wifi-enabled phone, be sure to test it at home first. A helper app, such as Fring, is sometimes required.