>I know that the most flexible option would be to give the user a memo field and let them do whatever. However, they want to keep the current "city, state zip" format intact for "domestic" companies and some alternate field(s) for others.

Memo field for address: bad. Formatted, validated entries: good. :)

>Current thoughts are to use a Country drop-down that would let us "toggle" which address fields are enabled.
>
>I really need to hear your comments and suggestions. TIA.

My one thought, (some will say I'm over-complicating the interface):
I'd have them choose the country on one form (a dialog?), then go to the appropriate, separate address entering form for that country, rather than have one address-entering form which swaps different TextBoxes (or containers of TextBoxes) in and out based on the country selected on the form.

As you learn the various countries' formats for phone numbers and post codes, you can create TextBoxes or TextBox classes with appropriate input masks for those countries' address forms.

My US$.02 (or less).

Cheers,
Rich.