Cell phone voicemail greetings are generally more personal and casual than office phones. Consider a greeting like “Hello, you’ve reached [your name]’s cell phone. I can’t take your call at the moment, but if you leave a brief message, I’ll get back to you as quickly as possible.”
Nobody wants to listen to a long-winded voicemail. Keep your greeting short, simple, and concise. A voicemail message should pique a client’s interest and leave them looking forward to your call. Stick to the basics, explaining your company name, hours of operation, and when to expect a callback.

Expanding on the simple approach above, let the caller know who they've reached. This will not only eliminate people leaving voicemails by mistake, but it will reassure the caller that they have called the number they intended.
A word of warning: These greetings will not do you any favors if you're in the midst of a job hunt or work in a conservative industry. Always remember your target personas. If there's a chance they won't appreciate your sense of humor, opt for a straightforward greeting instead.