Inlet of Smartphone stand is large enough to accept other types of phones. It is also used as a stand for medical equipments with LCD display. Materila of this stand, soft rubber PVC will not interfere with electromagnetic wave from medical devices.
How large should inlet be? Considering the width of iPhone4S is about 2.31", the inlet of your Smartphone stand should be 2.36". When you have Smartphone cases such as silicone or polycarbonate the width of inlet should be larger by 5/32".