Google has announced its entry into the Mobile Virtual Network Operator and there are a lot of questions and talks around it. This project can have various outlooks to it. Some can argue that it a possible disruption in the industry as Google will refund, in the form of a credit, any money spent on data you didn't use. That's a significant change from the major carriers, whose revenues depend on charging a flat monthly fee for big buckets of data. Introducing this pay as you go service takes data fees into a new territory. But paying only $20 a month for Fi basics and each additional GB of data at $10, is only worthwhile if you already posses a Nexus 6. Project Fi does not offer any contract model so that means you will have to pay $649 for a 32 GB model, to obtain services of Project Fi.
One of the main factors which I observed can play a role in Porject Fi’s adoption rate can be the compatibility with other devices and not only one smartphone.
Another factor, which can play a role in Google Fi’s adoption rate, is the connectivity itself. Google has planned to start its project in the United States, and for the areas of the northeastern, which has excellent coverage from T-mobile and Sprint, it is a great deal. But if you move to regions like Montana then coverage can be a problem and hence it can play a role in customers adopting to the service.
Another factor which can play a role in the adoption rate of this project is the cloud service offered by Google’s Fi as it really makes it convenient for users to switch devices if you forgot your misplaced your phone beneath a couch sometime.
A relatively small factor will can play a part in its adoption rate can be the live customer service and tech support, since Goggle is not in this field too much so if they do not offer good service, it can show direct results from its consumers.

Google already has a strained relationship with the telecom giants and if it tries to by pass and become a network operator then it definitely poses a threat to telefonica. But its initial representation doesn’t make Google seem like it wants to become a network operator but will have to rely on the big telecom giants such as telefonica to move around and get its user base. So Google’s Fi initially does not seem to interfere much with telefonica’s workings. So I would say Google is more of a threat to the pre paid plans offered by the telecom companies rather than the whole institution itself.
Google seems to go more on the technical route of hardware and trying to provide the best cellular activity available by switching between operators and Wi-fis available (the strongest signal available at the point of time)

It is perfectly logical that Google would eventually be interested in acquiring some of its own wireless spectrum, although how it might go about that remains far from clear. Regardless, obtaining wireless spectrum could enable Google to leverage whatever technological advances its looming wireless project presents, assuming they prove truly disruptive. Google’s fiber went on the path of doing the same so it can be possible that what seems like a sheep right now can in the later stages get bigger ambition and becoming a threat to the likes of companies such as telefonica.
At this stage maybe its too early to comment if Project Fi would be a direct threat to telefonica as a giant like telefonica can always introduce new services to keep and woo customers and there will be the state in their favour.