The rumors were actually true, as it turns out. Today Google has basically become a carrier in the United States, with the launch of its new service called Project Fi.
Although it will offer mobile services, Google hasn't built its own network for this purpose. Instead, it will act as an MVNO (mobile virtual network operator), using the infrastructure of both Sprint and T-Mobile.
This makes Google a pretty unique MVNO - and means devices connected to Project Fi need to support the network bands for both T-Mobile and Sprint. This isn't something every phone out there can do, so for now Google is only allowing Motorola Nexus 6 units to use Project Fi.

If you already own a Nexus 6, Google will send you a SIM card. If you don't have the phone, then you can buy one through Project Fi on a 24-month installment plan (with payments of $27.04 for the 32GB model, and $29.12 for the one with 64GB of storage). There's also the option to pay in full - $649 or $699, depending on which storage variant you choose.
For more http://www.gsmarena.com/project_fi_d...news-12004.php
Google source https://fi.google.com/about/