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Reminder: Project Fi doesn't offer simultaneous voice and data when connected to Sprint

Project Fi offers a lot of flexibility when it comes to networks, with seamless switching between T-Mobile, Sprint, US Cellular and Wi-Fi for calling, texting and data needs. While we've established that the switching isn't much to worry about and actually works quite well, the one shortcoming arrives when you go to make calls and use data at the same time when your phone is connected to the Sprint network.

Just like other modern phones that are running on Sprint proper, there's no simultaneous voice and data support when your Project Fi phone uses the Sprint network. So if your phone is connected to the Sprint network (which by design isn't made clear to you) and you connect a phone call, your data connection will cut out — so you can't search for that restaurant you're trying to book, grab tickets to the show you're discussing, or perhaps more importantly use your laptop that is tethered to the phone at the time.

This really is only a problem because your phone won't tell you what network you're on.

While this isn't any big revelation to those who have used Sprint for any length of time, it can catch Project Fi users off guard. Without the assistance of a third-party app (opens in new tab), you don't know whether you're on T-Mobile, Sprint or US Cellular at any given time — and you'll only find out that you're about to drop your data connection for a call right when you make or receive it. That can be frustrating and confusing if you're not aware of this limitation.

If you're connected to the T-Mobile network the phone will keep a data connection (using VoLTE or dropping to HSPA+) during a call, but if you're on Sprint it'll drop out immediately. US Cellular is actually more proactive about rolling out its simultaneous voice and data, so if you happen to be connected to its network you have a good chance of not losing your data connection — but the US cellular network is dramatically smaller than Sprint's, making it a much smaller issue to begin with.

It's a hurdle that Google can't really do anything about so long as it continues to let your phone automatically switch between networks — which is kind of a tentpole feature of the service. And Sprint's sluggishness of moving to VoLTE (Voice over LTE), which would rectify this situation, isn't helping. For now, your solution is to either make VoIP calls using the Hangouts app (yes, you can still do that), or be ready for phone calls to potentially put a pause on your data consumption.

Andrew was an Executive Editor, U.S. at Android Central between 2012 and 2020.

10 Comments
  • T-Mobile has VoLTE almost everywhere so it doesn't drop to HSPA+, it stays on LTE
  • My phone still drops to HSPA+ to make calls constantly. No carrier is at the point of having 100% of their network only calling over VoLTE.
  • I havent seen HSPA in years on Tmobile in Mass. Fi enabled it for me a year ago as well
  • Found this out the hard way the other day. Typically my Fi is connected to T-Mobile 24/7, but a Sprint tower must have been switched on recently near my office b/c it's full reception and always connected to Sprint now while at the office. Was on a call with Xfinity (yuck) and they had to email or text a verification code. Unfortunately neither seem to work while on the call so I had to hang up and have them call back. Thought it was something wrong with my phone so spent a couple hours diagnosing. Then researched online and found it was a Sprint thing.
  • I ran into this when I was using Waze while on a call and noticed it said something about the network not being available. Now I just force it over to T-Mo whenever I can, their signal and data speed is generally much better in my area anyway.
  • Sprint does know it's 2017, right?
  • Apparently this happens on T-Mobile too. According to Fi Info, I was on T-Mobile 4G LTE, but my data stopped. It doesn't happen with my T-Mobile SIM in the phone, but happens every time with the Fi SIM. On a Nexus 6.
  • It will not happen on T-Mobile as they are gsm. They use 2 radios. One for data, one for voice. Sprint is cdma, they only use one radio. Both data and voice use the same radio, therefore no simultaneous voice data
  • Thanks for posting this - I didn't know about it..
  • I remember that for some reason the old Samsung Galaxy S3 was able to keep a data connection during voice calls on Sprint (Boost Mobile) but was one of the few that could. Good old 2012. The later Tri-band model would not.