I feel the directions aren't clear. Is the entire formula below belong in the interest rate field? or should there be two formula fields. Thanks 
IF(Principal__c < 10000, 0.02,

 IF(Principal__c >= 10000 &&

  Principal__c < 100000, 0.03, 0.04))

 Principal__c  *  EXP( Interest_Rate__c  * (YEAR(TODAY()) - VALUE(YearStarted)))
)

Hi All,
How I can achieve this task in professional edition 
If user uses his mobile to call a customer and he has SFDC 1 app on his mobile. Will the calls get auto-logged and user can add details later.