Since AT&T is partnered with Yahoo for portal and other services for their DSL service, if MSN buys Yahoo, then the relationship between Yahoo & ATT would be over since MSN is also a DSL provider. What if...and this is just a WHAT IF, ATT decided to use Google for portal and other services? What kind of mega deal would that be! Just one of things that make you go..hmmmm....
Think about it! Google might be big but it's nowhere near ATT big! ATT could easily shutdown Google by taking down the backbone that Google's tied into. Little secret here. Many of the backbones, MCI, UUnet, etc., still use ATT lines. Can Google do anything to harm ATT? Nope!
Frankly anything can happens, these are two giants merging, they can even sell some assets to Google who knows, or they might divest of some subsidaries, infinite possibilities, very difficult to ponder over them.