New York-based Payfone offers a checkout and in-app payments service that lets users purchase digital and physical goods using their mobile phone number.

In its latest funding round, the firm has raised $19 million, with American Express joining as the largest strategic investor. Verizon Investments, Rogers Communications and existing investors Opus Capital, BlackBerry Partners Fund and RRE Ventures also participated. The money will be used to support expansion across North America, Emea, Latin America and Asia.

Payfone is also working with Amex to combine its authorisation and payment services with the card giant's recently launched digital payments platform, Serve.

Based on the Revolution Money P2P payments platform Amex acquired last year, Serve was unveiled last month, enabling users to buy goods and make person-to-person transfers online and through mobile phones. The Payfone partnership will let consumers link their mobile phone numbers to various payment methods and then use it to make online purchases.

Rodger Desai, CEO, Payfone, says: "Over 5 billion people worldwide currently have mobile phones, however less than 2 billion have credit cards. It's our goal to make the mobile phone number the new accepted way to pay."

Dan Schulman, group president, enterprise growth, American Express, adds: "The alliance is an important next step for the international roll out of Serve. We look forward to working with Payfone as we evolve the Serve platform to provide the most advanced payment solutions for buyers and sellers, while setting new standards in security, simplicity and reliability."