I found it on Amazon.
On the author's website:
"DON'T LET THE PRESIDENT HAVE THE LAST LAUGH! Danielle Crittenden's hilarious collection of imaginary online correspondence between the POTUS and his "buddy list" is now available in a dead tree edition by Simon Spotlight Entertainment. You'll find THE PRESIDENT'S SECRET IMs at Amazon and bookstores across the country."
Online, George "Dubya" is kickass43. He spends a lot of time on his computer talking everything from US foreign policy to his situation at home with the world's bigshots. Including ben16 (Pope Benedict XVI) and sxybritguy10 (Tony Blair). Hilarious fun.
Bill Clinton, true to form, is ladeezman42.