The capacity of POIs is only one of the problems on GPS devices. Searching, browsing, & finding POIs on a small screen with low resolution using a micro joystick-like device or small arrow buttons is tedious at best, if not impossible.
Compare that with the big screen, high resolution, & easy navigation on mobile device. There are some recommended apps for your device. They hold unlimited number of POIs, at least as much memory as you have on the phone.