newbie going to europe with questions!
 

We are headed to Italy, Switzerland, and France next month and will be in Europe for the very first time.

T-Mobile is my cell phone provider and I'd like to use my Samsung while there, primarily for text messages directed back home to the USA (I've already taken care of getting my account ready for international texts), but I'd like to use it a handful of times for actual calls home or to call ahead to confirm an arrival time along the way, as well.

After I have my phone unlocked what is the cheapest, most convenient, most reliable way to use it during our trip?

You have 2 choices - you can either use TMO's international plan and pay a LOT of money, or you can buy a pre-paid SIM in each country you visit. Read through this forum - you should be able to find your answers.

It's probably least expensive if you get a prepaid card in each country that you visit. Typically your initial card will have some credit on it. Also, if you're going to be in Europe it might be practical to roam in Europe since the EU mandated lower roaming rates between countries.

If you're concerned about people getting in touch with you it's possible to forward your T-Mobile US account through use of a service such as Kall8.

For Switzerland I would recommend Lebara Mobile, who charge $0.10 per international text and $ 0.09 per minute + $ 0.15 call setup-fee to the US. They currently give away SIM cards if ordered online. In local stores SIMs should cost $10-20 with some initial credit, so the SIM practically costs somethine like $5. Lebara is sold e.g. in "mobilezone" stores.

Just in case there's a misunderstanding in the OP: You do not need to unlock your phone to use it abroad with its present SIM, only to use it with SIMs from other providers. (I think you know this, the phrasing was just a bit ambiguous.) Unlocking a phone is always a good idea, and T-Mobile USA will do it for free (by providing an unlock code) if you're a customer in good standing; sometimes they ask for a reason, but "I'm going abroad an want to use a local SIM" is a good answer.

If you intend to use your phone VERY sparingly (ie, only a few minutes total) in one country, it might work out cheaper than a local SIM, especially in France, where there are no good options. (This also applies to an Italian SIM, which when roaming in France will not be that much more expensive to use than a local one.)

Italian SIMs are described in detail under "National operators", and there are plenty of forum discussions as well. To get one, you will need to generate a codice fiscale (already described on the Italy page) but this is no big deal.

One more issue to add to the excellent comments above: Make sure your phone will work in Europe. Most phones these days are quad band, but many lower-end phones are still only dual band and won't work outside North America. So make sure your phone operates on all four GSM bands, 850/900/1800/1900 MHz.

If you're not sure, post your phone model here.

Actually there are a couple of French MVNOs offering relatively cheap international calls, which I pointed out in this posting. But you are right of course - the search for a shop selling one of those SIMs and the purchase of the SIM won't pay off for 10 minutes of airtime.

Yes, you are right, they are ok options for someone spending a short time in France - I'd just mentally blocked them out because of the terrible expiration policy....