When Yingda Zhai was working on his PhD in Austin, Texas, he used to stroll through the neighbourhood he lived in not too far from campus. On these walks, he saw something that puzzled him, something that would set the course of his research for the next few years.
What Zhai noticed was this: his neighbourhood wasn’t that well-to-do, and lining the streets were shops like MetroPCS, Cricket Wireless, and FamilyMobile. These small cell phone companies, also known as mobile virtual network operators (MVNOs), offered cheap plans without any contracts or credit checks. But the snag was that they came with slower connection speeds, smaller network coverage, and without features such as phone tethering.