Google's Project Fi offers a sort of unlimited plan

"Bill protection" will help heavy data users cap what they spend.

Google's cell phone service, called Project Fi, is changing how its billing works. Previously offering a simple model of paying for whatever data you use, the plan now caps how high your bill can go if you tend to use a lot of data. This new "bill protection" comes with a catch: Google will cap your speeds if you cross a certain data threshold.

The plan scales based on the number of people you have signed up, but basically, you'll still pay $10 per gigabyte of data as normal for the first few GBs you use a month. If you're on a single-person plan, your monthly bill won't go higher than $80, even if you use more than 6GB ($10 per GB plus the $20 flat fee for calls and texts).

This feature is called "bill protection" and it's Google's version of the unlimited plans now offered by other major carriers. It's not truly unlimited. If you use more than 15GB, Google will start capping your speeds, though the company will let you opt out of slower speeds and pay for extra GBs above 15 at the normal rate.

While a speed cap doesn't sound great, the plan actually looks like a good deal for heavy data users without upping the price if you don't use data. You're basically getting GBs 7 through 15 free of charge. The price and GB cap change depending on how many people you have in your plan. Head to Project Fi's site for details.

Google's Project Fi wants to help you cap your bill.