Mobile carrier billing — paying for digital services through a phone bill rather than a credit card or bank transfer — addresses a payment need that is invisible in markets like the UK or Germany but essential in markets where credit card penetration is lower and where pay-as-you-go mobile is the dominant communication infrastructure. Fortumo was founded in Tartu in 2007 to build the technical and commercial infrastructure connecting digital service providers with mobile network operators globally. Its platform aggregates carrier billing relationships across more than 90 countries, giving digital businesses — gaming platforms, video streaming services, app stores — a single integration to enable mobile payment in markets where it matters most. The company powers carrier billing for major global digital businesses including Google, Spotify, and Microsoft, processing billions in mobile-billed transactions annually. Fortumo was acquired by Boku in 2020, integrating its carrier billing infrastructure into one of the largest global mobile commerce platforms. The acquisition reflects the consolidation of the carrier billing infrastructure category — the underlying technology and commercial relationships are difficult to build at scale, creating natural concentration around a small number of operators with global coverage. In the European fintech landscape, Fortumo's trajectory from Estonian startup to Boku-acquired global infrastructure provider is one of the more substantial outcomes for a Tartu-based technology company.