I once discussed this question with native English speakers. This is what they say: Till is rarely used. It's in poetry and song, probably because of rhythm as till fits better in some cases than until. In conversation you may hear it. (How long will you be there? Till 10 or so.) It's rarely if ever used in writing, unless someone is quoting conversation. Stick with until.

Till is a variant of until that is acceptable at all levels of language. Until is, however, often preferred at the beginning of a sentence in formal writing. There is not difference at all in both the words.

when i´m talking with american friends... they write "till" through msn .. to say until... maybe to write more fast, i guess--..

formal and coloquial and is UNTIL not UNTILL

Like what both other responses that you recieved on your question, 'till and until are both correct in using for a response - more so in written form... Hope that this helps to clarify any doubts that you have...