the first two digits
These used to be words time back way back. Example, my phone number of youth was LAkeview 5-xxxx. Before that it would have been LAKeview-xxxx. Nowadays it would be 525-xxxx. New exchanges, when created, didn't have that restriction applied to them. Area codes were always of the form n0n or n1n because they *weren't possible exchanges, 1 and 0 not having letters associated with them. That has all gone out the window, defenestrated by the ravages of overpopulation and burgeoning phone requirements.
Companies give out their numbers as all letter combinations such as 1-800-MATTRESS because they are easy to remember. The fact that they are harder to dial can be handled by writing the number down just before you call and converting to, in this case, 1-800-628-8737. It's easier to handle this somewhat tedious process with pencil and paper than it is with finger and keypad.
Remember, convert, dial.
