Under the agreement, a high-speed wireless broadband service will be made available from ten Cashbox sites.
The company, which was founded in 2003, has 2,500 ATM locations across the UK, with machines in London, Manchester, Glasgow and a number of bars and restaurants in the City of London.
Any customer with a wireless-enabled device will be able to access the service to surf the internet, pick up email or make voice over internet protocol calls using BT Openzone.
There are currently around 4.8 million BT broadband customers with inclusive Wi-Fi minutes. In addition, users of the O2 iPhone have access to over 3,000 BT Openzone hotspots included in their plans.
Users of BT Openzone roaming partners like iPass and Boingo will also be able to access the ATM Wi-Fi feature.
Cashbox chief executive Ciaran Morton said the deal is part of the company's ongoing drive to extend its service offering and provide customers with "additional opportunities" to use its ATM machines.