A printed monopole slot antenna for WWAN metal-ring frame (MRF) smartphone applications is presented and studied in this paper. The greatest highlight of the proposed antenna is that the band of 824–960 MHz scarcely affected by the modified MRF and achieves great stability. The MRF resonance is also utilized to enhance the bandwidth of the upper band of 1710–2170 MHz. With small size of 8 × 40 mm2 occupation and wide band coverage, the proposed antenna is a promising candidate for the MRF smartphone applications.