Press "Features" scroll down to "Phone User", press select, scroll down to "Self administer", press select, scroll down to "Abbreviated dial", enter the number to dial and then press the button were you want to store the action.
Another option is to read the phone manual.
You can store a part of a number and manually dial additional digits.
So if you want to dial any number between 019005500 to 019005599 then store 0190055 under a button.
Press the button and manually dial 00 to 99 as desired.