Quite correct, I'm not sure which mobile phones Shane has been using, but every Nokia I have ever owned has supported maual network selection. Currently that's an N95, so a reasonably new smart phone.
I'm actually sad enough that I've checked out the tariffs in advance before travelling abroad and made a list of preferred networks to use! (Getting the tarriffs can be a bit of a battle though!)
Oddly enough when I was in France a few years ago it was better for me to use any network other than Orange FR... Even though I'm an Orange UK customer!