A wavefront-coded imaging system employing a spatial light modulator (SLM) for the agile implementation of phase masks is presented. The SLM is a liquid crystal display that can be modulated to implement cubic phase masks of variable coding strength. These phase masks produce broad point spread functions insensitive to defocus aberration and are used in combination with post-detection digital image processing to extend the depth-of-field of an imaging system. A detailed description of the calibration process of the SLM in phase mode is presented together with experimental results which include wavefront-coded modulation transfer functions and increased depth-of-field images. The most interesting feature is the versatility provided by the imaging system, as compared to conventional (fixed phase mask) designs, and the agility in which it is done.