Previous research concerning the use of cell phones indicates that physical manipulation of the phone in conjunction with the cognitive need to compose a message together contribute to driving performance degradation. We have suggested that automated assistive text entry schemes such as Nokia’s T9 may mitigate some of these identified costs. In this work drivers in a simulator drove and texted using either the assistive T9 system or an unassisted multitap system. Contrary to previous pilot findings participants showed greater degradation of driving performance when using the automated assistive T9 than the unassisted multitap. Findings support the idea that cognitive composition of a message combined with entry interface automation contributed to driving performance degradation. It further implies that the costs of that automation may exceed the benefits.