Just leave them alone. It's a quirk and really doesn't make any difference
to the useability of Outlook. I know it looks messy - all of ours do too.

I want them removed.  When I transfer my contact to my Palm 700 and load it
into my car.  My car does not recognize the parenthesis;  therefore, it is
unable to dial the telephone number from my contact list.

I need to do this to sync outlook with my phone. Some options are

1) Delete anything under:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Telephony\Locations

eg, location1. However, this will cause a modal dialogue to appear if
you attempt to edit a contact's number in outlook, which you will then
be required to complete, bringing back the parentheses. May also break
your dialing setup/modem etc

2. Create a new location with an areacode that is the length of the
longest number in your contacts eg, for a 10 digit number use
1111111111 (you could also do this by editing a "locationX" key in the
registry as per above). Set your contacts to use this as the location
(perhaps save under a differnt country to identify). The new location
will happily coexist with your others.

HTH