The Retevis Walkie Talkie Set of 4 includes a mix of RT22 and RT21 models, both of which are UHF band calling systems. With a total of 4 channels available, this set is perfect for communication in various situations. The Retevis brand is known for its quality products in the world of radio communication, making this set a reliable choice for those in need of a dependable two-way radio solution.