Can wireless products sold in the United States be used in other countries?

In general, these products will work as long as you can supply the proper AC power requirements, as long as you have a "matched set" of components, i.e. AP or wireless router and client adapters. Intermixing U.S. and locally-sourced products, can be a little trickier, however.

802.11b and 11g products, which operate in the 2.4GHz frequency band can be used without technical or legal problems. However, channel selection limitations must be observed.

The situation is more complicated for 802.11a products, which operate in three 5GHz frequency bands. The issue, again, is mixing U.S. and locally-sourced products, which might not interoperate due to channel selection limitations.

This article provides some good insight into the issues.