We run online contests and want to eradicate cheating (yeah right), or at least mitigate it. I've asked the question regarding user experience here: http://ux.stackexchange.com/questions/15980/ways-to-avoid-online-contest-voting-fraud-is-sms-account-verification-too-much/15991#15991.
Now I want to know about the viability of my original premise: people typically only have access to one phone number that can receive SMS messages; they cannot create numerous viable numbers on the fly. Is this true?
Background: I understand that Google Voice and Gmail both allow users to send/receive text messages through numbers Google assigns. In the case of Gmail, you cannot receive texts from a number you have not previously sent to; the outside sender just gets an error. And Google in general does not currently recognize short codes as valid, so you simply can't send to them at all. So, "viability" of a number to us means that it can be used with our short code system.