"Note: Sent from my iPhone. Please excuse any typos."
"Typed with big fingers on a very small keyboard."
"Sent from my phone. Please forgive any grammatical humors."
You know what? No. You do not get a pass for not proofreading your work just because you are using a mobile device. If you're sending a professional email, be professional.
"Please excuse any typos"
"Excuse my typos, I refuse to bother to take the time to re-read what I've just dictated or typed"
"I don't give a shit about the correctness of this message."
Take some responsibility on every communication device you use. Period.