why did apple change the address book to just two panes for osx lion?

All anyone here can say is "because they did". None of us are party to Apple's design decisions. You can comment to Apple via their feedback page, if you wish:

http://www.apple.com/feedback/macosx.html

There is no hack I've seen to bring back the option. I seem to recall posts from people who'd attempted to use the Address Book application from 10.6, but I don't recall if any of the attempts were successful. As an alternative, you might take a look at Cobook:

http://www.cobookapp.com/

It's free while it's in beta, and many of us are finding it a great adjunct or outright replacement for the Address Book application. It may not fit your needs, but it might be worth a look.

Regards.

It is still there. Just hidden. Quit Addressbook, and open Applications -> Utilities -> terminal and type:

defaults write com.apple.addressbook ABShowDebugMenu -bool YES

Next open Addressbook, and select "Show Classic Window" in the Debug window.

Special thanks to this page and its user feedback for the tip: http://www.libertypages.com/clarktech/?p=2326

That option no longer exists in Address Book in OS X 10.7.3.

Note, the above link says it might be gone with 10.7.1, the debug menu, but I don't have access to my 10.7.1 machine until later to test this trick out.

OK, thanks. Then all I can say is issue a http://bugreporter.apple.com/ report as a developer that it is desired. http://developer.apple.com/ is where you can sign up for a free developer account.

i dont undersatnd why they took something that was working fine and than took away features.

For what it's worth, Apple listened and the next version of Contacts will have a three-pane layout;

http://www.macworld.com/article/1165436/mountain_lion_hands_on_with_contacts_and _calendar.html