Accessible mobile phones for people with physical disabilities is an area that is still developing with new products and services emerging to assist these people to access the telecommunications equipment that is currently available. This research evaluated the effectiveness a prototype interface system for a mobile phone and accompanying speech generating device that enabled the user to independently initiate, answer, conduct and terminate voice calls and send text messages through the use of their communication device. Separate trials were conducted with two teenage participants with a physical disability who cannot speak and require a communication device to communicate. After their respective trials, both participants recorded very high overall performance and satisfaction outcomes. This paper highlights that involving the end-user in customization of the interface system during the trial had resulted in a very successful outcome. The trials demonstrated that people with severe mobility and speech impairments are able to effectively use a mobile phone in its many modes of operation. The trials affirmed that the system has given the participants a sense of independence, safety and security, and also contributed to improving their communication skills, leading to the self confidence to engage in conversation and social activities.