Teen pop sensation Justin Bieber is scheduled to appear on MTV's "Punk'd" this week, and his love of a good prank is well documented.  But a prank the singer recently pulled on his fans via Twitter may end up being a costly mistake.  Earlier this month, Bieber posted a randomly chosen phone number on his Twitter account, minus one digit, with the caption "Call me right now."  A good-sized portion of Bieber's 19 million followers on the site began calling numbers, guessing at the final digit, and a pair of Texas residents received more than a thousand calls each as a result.  According to a report from The Hollywood Reporter, the two people have consulted an attorney and are considering filing a lawsuit over the prank.