If you just want the LOOK of () and - then use the format option in Excel because this will show the () and - but the cell value will remain unchanged, thus keeping the number in tact as a number (I recommend this).
If you want to physically ADD the () and - then use the formula I provided and then copy and paste special values over the column with the 1112223333 (Though I don't recommend this).
If you highlight all your cells, then in the formula bar insert your mouse to where you want the first symbol. Then with the cells still highlighted, go to the insert ribon, then insert special symbol icon (looks like an upside down horse shoe and click on the first side of the parenthesis from the symbols shown. Press insert, then close and then control and enter. All the numbers will have opnbe side now do the same for the second side, and if you want to enter a space do the same and on the symbols menue theres a blank white cell in there. Click on that to add the space, again press insert then close and ctrl and enter to put the space into all your cells.
It's fairly quick way, abount 9 mouse clicks. I got Excel 2007 so not sure where that menu sits in other versions
Actuall forget all tha stuff i just typed-if you highlight your data, then in the formula bar just enter the correct symbols and hyphon where you want them and press ctrl and enter it will apply it to all of them. kinda mucks it up as a useable number though after that
i tried posting this and it got stopped.....but just highlight all your cells, in the formula bar add the parenthesis where you want them and a hyphon as well if you want, then ctrl and enter to apply that to all of your data.