Infobip
Infobip's TAM in 2006, analysed superficially, seemed modest: the European business SMS market was limited in size, margins were low, and enterprise customers preferred to deal directly with local operators.
The real SAM Infobip had identified was different: companies operating across multiple countries that needed a single provider to send transactional SMS (OTPs, notifications) reliably and traceably. A much smaller segment of the total, but with a much more acute problem and significantly higher willingness to pay.
The SOM in year one was smaller still: European tech companies that already understood the value of a unified communications API and had the technical capability to integrate it. A market of a few hundred companies — but the right ones.
Infobip's TAM/SAM/SOM lesson is precise: the "global enterprise communications" TAM today runs into hundreds of billions. In 2006, using that number in a pitch would have seemed delusional. Building from the right SOM towards the SAM, and letting the TAM become visible as the network expanded, was the only credible sequence.
A credible TAM is not declared — it is demonstrated through the SAM→TAM sequence. Present the SOM you can capture today, the SAM you become in 3 years, and the TAM as logical consequence.