Google Fi Market Sizing: Addressable Phone Lines and Annual Service Revenue

Estimate the size of the market for Google Fi, the mobile phone service that Google sells directly to consumers. Explain how you define "market size" for this product, lay out the equation you will use, state each assumption with a round number, do the arithmetic, and finish by checking whether your result is believable. ```hint Let the business model set the filters Fi sells service on networks it does not own and expects customers to bring or buy a compatible phone. Use those facts to decide which phone users truly belong in the market before you put a price on them. ``` ### Clarifying Questions - Should the answer be a number of phone lines, annual revenue, or both, and do phone sales count or only service plans? - Is the scope the United States, where Fi is sold, or should international demand be included? - Do you want the total market for this kind of phone service, the slice that Fi's model can serve, or the share Fi could realistically win in the next few years? - Should business lines, tablets and smartwatches be counted, or only consumer phone lines? ### What a Strong Answer Covers - A clear definition of market size that matches how Fi earns money, including whether lines or revenue are being counted. - An equation that moves from people to phone lines to revenue, with a reason for each filter (network coverage, device compatibility, willingness to leave a major carrier). - Assumptions labeled as such, rounded for easy math, and arithmetic that stays correct across monthly and annual figures. - A sanity check against an independent reference point, plus the assumption the answer is most sensitive to. ### Follow-up Questions - Which single assumption moves your estimate the most, and what data would you use to pin it down? - How would a bottom-up estimate built from Fi's sign-up funnel compare with your top-down figure, and what would you do if the two disagreed by a factor of three? - If Google wanted to double Fi's subscriber base within three years, which segment in your model would you go after first, and why?