It's 2014 (almost 2015), you don't need to give your personal number. Google Voice is free and seems to work but can't confirm since the last text posted was at 12:28 pm. Bonus, one can use their PC with a real display and keyboard if use their GV number.
It wouldn't be a texting only to post site then would it? My point is there are free services where one can get a second phone number for uses like this.