Till or 'til?

Here's one that even Yahoo doesn't seem to know (neither does Sonic, so they're in good company). The abbreviation for the word until is till. Not, as Yahoo would like us to believe, 'til. Interestingly, the spellcheck on my iPhone tried to change 'til to 'till. Also, not correct.

Will people know what you mean if you use 'til or 'till? Sure! But why not be right (I like being right!) and use till?