can't activate my Iphone

Do you recognise anything about the email address, have you had a yahoo.com mail address starting with 'r' ? If it's your account then you could see if you can get access to it via http://iforgot.apple.com

Or did you buy the phone used, in which case could it be the previous owner's account - if it is then you will need to contact him/her to remove it from their account : http://support.apple.com/kb/TS4515

You don't know what the email address might be ? Do you know if you made any purchases on the account, and if so are they still on your computer's iTunes library : http://support.apple.com/kb/HT1920 ?

If not, and you cn't get access to it via http://iforgot.apple.com, then you could try contacting Support in your country and see if you can get access to the account that way : http://support.apple.com/kb/HT5699

But until you can get access to the account you won't be able to use your phone