Google is running a new promotion from now until March 24 to tempt people onto a Fi contract. New users porting a phone number to Fi get a month’s usage for free, saving you between $20 and $80, depending on how much data you use.

Phones can’t have been bought through fi.google.com and the existing number must be ported during the signup. The existing number must also have been active since December 8, 2018.

Additionally, this has to be the full Fi service, not just the $10 data plan, and the devices must be active on Fi for 30 days for you to qualify.

The free month will be applied as credit on the next bill which covers “a single subscriber’s unlimited talk and text, data usage, and taxes and fees for one month.”

It’s available for U.S. residents only with Google Payments and Google Fi accounts.

Why Fi?

Google Fi, formerly Project Fi, is a cell phone contract exclusive to certain Android phones and iPhones. It differs itself from existing carrier contracts by only billing you for the data you use, so you won’t be paying a monthly bill for data you don’t make use of. As of recently, it supports RCS Messaging too.

With a Fi plan, you could already save more money than you would on a more traditional carrier contract, so this free month is just another way to sweeten the deal.

If you’re interested, you can view the eligible Fi phones here and check out some specific LG and Motorola phone promotions at this link.