Originally commissioned by AT&T (The American Telephone & Telegraph Company) in 1976, Bell Centennial replaced Bell Gothic as the new typeface to be used in AT&T's phone books. The change in typeface was due to printing and visual problems that Bell Gothic brought along after a swap in printing methods in the later years of phone book production.
To create Bell Centennial, Carter made a few changes to Bell Gothic:
1. Name & Number face became heavier and wider, increasing its prominence over other information
2. Width of the less prominent Address face was decreased
3. Increase in stroke width to prevent the letterforms from breaking apart
4. Letters were further apart (more breathing space), to prevent letters from bleeding together on the page
5. Added in notches at the corners of the character to prevent bleeding
Apart from changing the widths and thickness of the typeface, AT&T wanted Bell Centennial to have a more modernistic feel and be a typeface that could match with Helvetica, the typeface that AT&T was using in its corporate publications.
Helvetica was not used in AT&T's phonebooks because of its closed letter shapes. It could not be read when the font size is extremely small (e.g. Size 6)
Bell Centennial is still only used as the typeface for phonebooks until today.