Through March, Sprint is quadrupling the reward it offers to subscribers who get their friends to sign up and activate an account.

Customers who refer a friend to Sprint before March 31 will be eligible to receive a $100 Sprint Referral Rewards Visa debit card worth $100, while the new subscriber will get a card worth $25. The standard reward for referring a new Sprint customer is a $25 debit card for both the referrer and the new member.

To claim the reward, new subscribers must buy and activate a Sprint or Nextel phone by the end of the month. They then have 15 days to use their phone to call Sprint and give them the Sprint phone number of their referring friend.

Sprint customers can go here to submit the e-mail addresses of their friends. Sprint will then e-mail an invitation to join the service, including news of the $25 debit card reward for registration.