I removed the standard one on my device. The point of the "Sent from my iPhone" thing is to explain typos, right? I don't want it to be clear to partners or clients that I wasn't in the office when an email was sent, and I don't think that using an iPhone is a good excuse for typos in work correspondence anyway because you should be proofreading and such, so there's no need for a disclaimer. And I don't know why friends and family would need to know that an email was sent on my mobile device.
I don't think I've ever seen a mobile signature that I thought was clever.
BIL has a signature from a video game that says "android hell is a real place, where you will be sent there at the first sign of defiance." It suits his personality, but I hope he doesn't use that account professionally!
I just deleted the standard signature for my phone.
There's a girl on ML that has a sig that says "sent from your mom" or something like that. It cracks me up.
As for e-mail sigs, I use a standard sig with my name, company, and contact info for work e-mail, and in my personal e-mail I use no sig, I usually just type something depending on who is getting the e-mail.
I HATE getting professional e-mails that say "Sent from my iphone" and crap like that.