Judging by the majority of the business cards I currently have littering my desk and note board, I think 'cell' or 'c' would be the most commonly accepted abbreviations. But I have also seen 'remote', 'rem', 'mobile', 'mob', 'm', and 'clr' used.

I always refer to my cell as my 'mobile' phone. But, for a businesss card I would go with 'cell'.

In Germany, I mostly use the mobile net the cell-phone-user is in, as it is an added information (calls from d1 to d2 are more expensive than d2 to d2 and so on)
So I often end up using D1 or D2 as abbreviation. It doesn't work so wel with the E-net, as it is confusing (although no one would thing of a phone number as an eMail-address :-))

As long as you don't call it a "handy."

"Cellular" is a specific technology, like 3G or PCS. So "Mobile" is more generic, and often a more appropriate term.

For cards I prefer M or MOB or Mobile.