Can I use my iPhone as an iPod in another country?

I am going on a month long trip to Japan and would like to bring along my iPhone 4 to take pictures with, listen to music, etc. The only problem is that I don't have international services. So I figure I can take out the SIM card and it will be an iPod touch, right? My problem is that I don't want to come home to a big fat surprise bill. Thank you.

Not the iPhone and not the iPad internet if you use the 3G you pay for

When roaming in another country, iPhone and iPad will automatically select the best network for use while roaming. However, you can manually specify a network using the following steps:
Tap Settings > Carrier and turn off Automatic. Wait until available networks appear (this can take up to two minutes).
Tap to select the carrier you wish to use.
Return to the main Settings screen.
Note: This setting may appear only when you're outside of your carrier's network and other local carrier networks are available.

If you do not have an international data plan, turn off Cellular Data and/or Data Roaming to avoid data roaming charges:
iPhone: Tap Settings > General > Network
iPad: Tap Settings > Cellular Data

When data roaming and cellular data are off, you should not see a cellular-network indicator in the status bar.