can you take out the iPhone's sim card and use wifi outside of america?

gentmatt's answer is correct, however if you don't need to make phone calls at all you can also just turn on airplane mode. I have done this many times abroad. Turn on airplane mode in settings, then turn wifi back on. Your cellular signal stays off.

Yes.

You can use your iPhone's Wi-Fi without a SIM card, no matter where you are.

If you still want to be able to make calls, but avoid celluar data (data roaming) you can choose to disable just this feature.

You can get further information from Apple's support website at iPhone and iPad: Using cellular networks while in another country.

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.