I think typos such as Yhaoo are harder to come by on a moble than you think.
yagoo is more likely than yhaoo because users using multiple punches to a alpha/numeric key are more likely to loose count of the keypunching than to miss the number alltogether.
For example, "yahoo" on a mobile is 999244666666 while yhaoo is 999442666666 while "ybhoo" would be 999244666666
Make sense?
Of course, that all goes to pot if they have a QWERTY cell phone
GoPC