The phone number directs the message to a specific phone. 123 has a specific meaning I'm not aware of.
You see this a lot for poll taking. For example, during Red Sox games on TV they have a poll. They ask a question as part of an ad and tell you to text your answer to a certain phone number. e.g. "Do you think the Red Sox will make it to the playoffs this year?". Text 1 yes or 2 for No.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan