He has the white I phone but would like my black one, how can we do it making sure that we do not loose the information on either phone ?
I'm assuming both phones are on the same version of iOS. If not you need to make it so.
Sync each phone to its computer. Then right click on the iPhone's name in the list on the left and choose "backup" (still on the same computer).
Swap the SIM cards.
Go into iTunes Preferences on each computer, Devices tab, and check the box to prevent automatic syncing.
Connect your brother's iPhone to your computer. Right click on its name and choose "Restore from Backup" (this is NOT the same as the Restore button). When that finishes click the "Sync" button.
Connect your iPhone to your brother's computer. Do the same 2 steps.
What you are doing is very similar to these instructions: http://support.apple.com/kb/HT2109 - you are just doing it twice.