iPhone and iPad use the same dock connector as the iPod, so accessories can be used with either iPhone, iPad, iPod, or even Apple Watch. Nowadays, with Apple AirPods, it only gets easier.
Moreover, Apple created a special label "Made for iPod" which means that these accessories can be used only with this product.
Those products for iPod has been certified by the developer to meet Apple performance standards.
All in all, you may use all the dedicated accessories, which are officially proved to work with particular Apple devices.