I'll say it upfront: The most remarkable thing about Project Fi is how much it feels like every other cellphone carrier.

That may sound plain and boring, but it's no small achievement for Google and its attempt to undercut Verizon, AT&T and other wireless companies.

With Project Fi, Google has developed what for most city-dwellers will be a cost-effective and reliable alternative to traditional cell service providers. Although it comes with trade-offs that could deter some — such as power users of Google Voice or those just becoming acquainted with large smartphones — the service also offers a glimpse of what the future of mobile telephony might look like. And it's an exciting vision.

Google is leaping into the wireless business with a brand-new technology, one that lets you jump from WiFi to Sprint's network to T-Mobile's, without ever hanging up your call. This type of seamless handoff is what allows Google to charge subscribers as little as $30 a month for unlimited talk, text and 1 GB of data. Whenever possible, calls are routed over WiFi, which costs Google (and therefore you) practically nothing.

The rest of the time, calls and data are routed over cellular infrastructure rented from Sprint and T-Mobile. Both of those carriers independently support WiFi calling, but Google's service is the only one that lets customers hop between them in addition to relying on WiFi. And in my tests, everything on Project Fi just worked. No calls got dropped, and switching networks didn't cause any interruptions. Call quality was pretty crisp both in Washington and Vermont, where I tested the device. (I even did a radio interview from it, and nobody yelled at me for calling from a cellphone.)

The ultimate head-to-head test came as both my Project Fi phone — a Nexus 6 — and my existing iPhone sat side-by-side on my desk at The Washington Post. Sitting in the middle of the newsroom where service is weak, my iPhone will frequently fail to detect incoming calls to my Google Voice number, particularly if it's connected to the sluggish WiFi rather than mobile data. So I was curious as to whether the Nexus would experience the same issue. But the Nexus 6, running on Project Fi, had no problems taking Voice calls at all, no matter what network it was on. Incoming Google Voice calls would cause the Nexus 6 to ring off the hook, while the iPhone stayed silent and oblivious to the attempts to reach me.

There are other benefits to the invite-only Project Fi that make managing your account a cinch. Once you've been selected for service, you get access to a dashboard where you can change the size of your data plan whenever you want. Once a month, you can decide to put your service on pause. Although you'll lose the ability to forward calls with your Google Voice number and you won't be able to access mobile data, make calls or send text messages anymore, you'll get a credit added to your account for each day you keep the service deactivated. You'll also get a credit back for the cost of the data you bought but didn't use over the course of the month. You can even set up your Nexus 6 as a mobile WiFi hotspot and allow your laptop or tablet to surf on your phone's data connection at no extra charge.

Project Fi's stance on data is so generous that if you travel to one of 120 supported countries, you'll be able to surf the Web without incurring any roaming fees. Google slows your speed to roughly dial-up rates in these locations, but if you're lost in an unfamiliar city, having that access can be reassuring.

At the same time, Google requires subscribers to make some concessions. The Nexus 6 is a gigantic phone — and it's the only device that will support Project Fi for the foreseeable future. Here's what it looks like stacked up against my iPhone 5:

Google has been slammed with requests for Project Fi invites, so the decision to make the service a Nexus 6 exclusive — driven probably by Project Fi's hardware requirements — likely isn't hurting its popularity. Still, Google could have expanded Project Fi's appeal by making it available on the hugely popular Nexus 5, which is smaller and widely regarded as an incredible deal for the amount of technology packed into the phone.

And then there's what happens with Google Voice. If Google detects that you have a Google Voice number when you finally register with Project Fi, it prompts you to assign that number to your Project Fi phone. If you'd rather not and ask to use a different number instead, Google will take away your Google Voice number — "no getting it back," Google's registration page says.

This could be problematic for people who give out their Google Voice number to acquaintances and reserve a different number for close friends and family, as I do. What Project Fi effectively asked me to do was to make a choice: I could start giving my personal number out to everyone I met (by porting my personal number over to Project Fi and giving up my Google Voice number) or force everyone to call my Google Voice number. I also wasn't able to record incoming calls anymore on this version of Google Voice.

How Google has chosen to integrate Voice into Project Fi sheds some light on the search company's plans for both services moving forward. Google Voice is increasingly becoming less of an application in its own right and more of a back-end technology that powers Project Fi and Google Hangouts. Meanwhile, Project Fi will have a big role to play in Google's emerging telecom play, helping it bridge the gap between mobile Internet and mobile voice service.

Then there's the biggest trade-off of all, which is that your use of Project Fi gives Google the ability to mine your usage data in all the same ways that Google's other services do. You can, however, choose to keep that data siloed within the Project Fi experiment: Google commendably lets you choose whether to let other Google products use insights gathered from your Project Fi participation.

Google's cellular service asks subscribers to make some choices that other carriers might not. But the company is betting that adventurous early adopters won't mind playing by those rules if it means being able to try the cellular industry's most ambitious WiFi calling program yet.