Hi Roger,
I would recommend that phone numbers always be text,
whether you left or right justify them, you will be able to enter
phone numbers of any country and have the most flexibility.
To change your phone numbers in place you can use a macro.
There are a couple of macros in
http://www.mvps.org/dmcritchie/excel/join.htm
Fix Local Area Phone Codes (#fixphoneareacode)
insertprefix will insert a prefix of your choice in front of TEXT,
which is what you see as opposed to values, or formulas.
If not familiar with macros see my Getting Started with Macros
http://www.mvps.org/dmcritchie/excel/getstarted.htm
I do not include this blurb when posted in excel.programming
Be sure to practice usage on a copy of your worksheet, to prevent
loss of data, and to make sure it fits your situation. .