The best lessons in life are those you don't have to learn first hand.  Instead, learn from the poor guy who cranked up a cell phone bill of $1,229.91 while traveling abroad because he didn't turn off the international data roaming. This sobering post from the travel blog Gadling ought to be required reading for every international traveler. It gives a terrific (and terrifying) snapshot on how cell phone charges can go so wrong, so fast:

"The technology behind all of this is mind boggling. Of course, everyone knows that it is expensive to "roam" when you are abroad, and most people use their phone judiciously. There is nothing wrong with making the occasional mobile phone call back home from Europe, or using it to call your airline to change a reservation when you are stranded thousands of miles from home; the $2-per-minute charge is something you can deal with.

Mobile International data is different. The cost of "International Data Roaming" borders on insanity. AT&T charges $19.50 per Megabyte of transferred data in most countries, T-mobile is only slightly cheaper at $15.36 per Megabyte. "

Got one of those groovy new iPhones? Lucky you! Now take a deep breath and read on:

"Things get worse when you use a 3G phone (like the new iPhone). When you can download faster, you can also run up a massive bill much faster. Imagine landing at your sunny destination, and turning on your iPhone. The phone instantly begins to download all your email, updates the weather, and fetches the latest prices of your stock portfolio. With 3G speeds, you'll be able to download information so fast, that you'll be paying around $60/minute. If you have an awful lot of email, then by the time you reach passport control, you'll owe AT&T $500. "

Be sure to read the whole post to get the full impact of the danger lurking in your phone. You'll also learn why T-Mobile beats AT&T when traveling outside the country.