entering s'pore phone number for u.s websites

Singapore
November 12, 2008 9:37pm CST
sometimes when i register to join u.s. sites, i'd be asked to give my phone number, and sometimes it is required. however i don't know how to enter my s'pore phone number in the format xxx-xxx-xxxx (the standard format for u.s. phone numbers). Anyone have any idea on how to do that? thanks so much in advance.
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