Finding a Gmail Account Associated With a Phone Numberby Andrew McClain
It happens to everyone at some point: you forget your account name, and no amount of typing, guessing and pleading helps you remember it. For your Gmail account, you can use your Google Voice number, which is associated with your Google account, to look up your account name. Google sends you your account name after you enter your phone number and follow its security protocols.
Go to the Google "Forgot Username Assistance Page" (see Resources).
Type your Google Voice telephone number in the "Number" field.
Type the displayed characters in the "CAPTCHA" field. You receive a message over your phone with your Google account name information.