New Fring is associated with Mobile number and not with user name, to get the previous contact you have to merge it with the new fring below is the process -

after new version is installed and activated with you mobile number to to fring web site http://www.fring.com/fringout

after you click login option you can see there is a space to type you phone numbe associated with fring account make sure before you click get code fring is open and workig.

After code is received click merge account and you will get a page to insert code and old user name and password.