Using an iPhone in a foreign country?

I will be traveling internationally shortly and wish to use my iPhone 3GS on a Wifi network, but not my 3G plan to avoid substantial roaming charges. Normally when I'm in a foreign country, I leave my phone in airplane mode so I can't receive texts or phone calls that would run up my bill, but that also prevents me from connecting to a Wifi network. Is there a way I can turn off the phone/3G internet portion of my phone and still connect to a wifi network?