can i use one apple ids on different iPhones?

You can use one apple ID for multiple devices but the app store would probably give you an error when using it abroad because your ID is linked to the US store I am assuming. As for facetime and iMessage, if you use the same ID then they are already linked and your iMessages can be received by both phones. It will not be the same phone number but you can set it to your email and people can facetime and send iMessages via that.

Yes, yes, and yes. See: http://support.apple.com/kb/HT1495

Lawrence, the link you posted was for using multiple devices on one computer/iTunes, mainly for iTunes syncing. Do you know if there's a help page for using one Apple ID on multiple iPhones, particularly for iMessage purposes?

There's no tip that I am aware of. There are two ways to use the same Apple ID on different phones. First, on each phone you can just select or deslect the way that phone receives messages in Settings/Messages. But the better way is to create a new Apple ID and use it just for iMessage. Leave the phones sharing an Apple ID for the stores and content, but in Settings/Messages log out of that ID on one of the phones, and log in with a new Apple ID just for iMessages on that phone.

Thanks Lawrence! I have an iPhone 5 on iOS7 and just got an iPhone 5S for work today, and had issues with the iPhone 5S only showing my iPhone 5 number and Apple ID emails as Send & Receive options. I've actually already tried the first method you proposed, but now my 5S is showing "Waiting for Activation" on iMessage for over an hour, even after multiple attempts of resetting the phone and network settings.