Last week a Finnish newspaper wrote about a poor customer who had subscribed to a fixed price data plan and thought that it is valid also when abroad. Result: his phone bill had 2.300€ data costs compared to normal 14,90€. Earlier this year there were a piece of news about a user who had used roaming data worth 25.000€.
Although in cases above the reason might had been that user didn't know about the subscription details and was using data connections intentionally, it is highly probable that users use data connections abroad without understanding that. Many applications ask permission to use network connections automatically and sooner or later poor user don't know anymore how many applications there are that keep on pulling updated data from the network. When user is having fixed-price data plan and he is using his home network, there is no problem but when terminal connects to a roaming network problems will begin.
I feel I have to remind about a simple trick I presented last summer at Nokia's site. It might even make sense to productize "safe traveling with smartphone" solution and add also other features that people need when traveling; for example whenever I'm abroad I turn off all the unnecessary power-consuming receivers like Bluetooth and WiFi because I cannot be sure where and when I can recharge the battery next time.