Why is it still in beta. Hasn't it been over a year now?
Why does Gmail/Google want your mobile number? To sign up for a Gmail account they want your mobile number so they can text you the invite code. Why do you think this is?
"Get your invitation code
To sign up, enter your mobile phone number below. We'll send you a text message with an invitation code to create your account. If you've already received a code, skip to step two! "
www.gmail.com