Will you be taking a laptop, tablet or iPod Touch? Skype or FaceTime would be great if you have wifi access where you're staying and just need to check in occasionally. Not so great for emergency access. FaceTime is only for Apple-to-Apple connections, but it's free. Skype can be used with lots of devices, and is free as long as you're Skyping to another Skype account. I believe they charge if you connect to a "regular" phone number, but the price is quite reasonable.

I second jent103's Skype idea. We had our iPads with us this week when we went to the Czech Republic, Spain and Italy, and we were able to use the Skype phone call function for free. I had problems with my flights, so I called American Airlines, for free with this function. It was great.

Buy a prepaid international calling card from most kiosks or tobacco stands and follow the instructions on it for international usage.
Relatively cheap in Switzerland "Flash card" (one of the few things in Switzerland that are!)
I do this every time from Germany and Switzerland--beats $4/minute!

I have the Skype app on my iPhone and agree it is a great way to stay in touch. You can also purchase an inexpensive phone number from Skype to give to family at home so they can call you. Wifi is necessary but if you miss a call you will get a message and can call back when you have wifi again.
www.skype.com

I don't have a laptop/iPad/iPhone, so the prepaid international calling card sounds good. Do you have to buy one for each country, or can they be used for all? Thanks!

I second the calling card option - they're cheap and readily available. I THINK you need one for each country, but since those aren't countries I regularly visit can't say, but they come in different denominations, so it won't be expensive if you pick up one for say 5 or 10 euros in each.

Be sure and check with your hotel before using the room phone. Hotel policies differ greatly. You don't want to discover at checkout you were being charged exorbitant fees. We found pay phones to be an endangered species in several places we visited.

Calling cards are easy and cheap, but as violetduck points out, depend on your access to a land line. Depending on where you're staying, that may or may not be an issue (if you're staying in hostels, probably no access to a phone unless they have a pay phone in the public space). You could do a calling card and/or try to Skype at internet cafes.

When I bought calling cards in the UK, they were UK-specific. You can get them at places in the US (I would imagine in Canada as well), and you might be able to use those in multiple countries, but they might not be as cheap. My calling card experience is about a decade old, though, so I'm not 100% sure.

Another cheap option is to just go to an internet cafe and they should let you make a VOIP call for pennies a minute.

www.ricksteves.com has a lot of helpful information about calling. Click on Plan your Trip, then Travel Tips and go down the page to Communicating.