On of the main reasons mobile phones are moving up to 24 and even 39 Ghz is the lack of available spectrum at 7 GHz and below.
Right now GSM mobile use 850, 900, 1800 and 1900 MHz bands. 3G and LTE have added some more bands in the 700 and 2100 MHz bands and LTE band 7 is 2600-2700 MHz.
GSM is largely superseded but the SIM card remains as the legacy of separating the service from the handset allowed for innovation that nobody could have seen coming.
The problem with 24 GHz is that signal propagation into buildings is very poor. The main advantage for these frequencies would be in stadiums and open area arenas where a relatively dense array of transceivers could be installed too handle the short range inherent with SHF and EHF signals. The broad number of channels would allow for tens of thousands of simultaneous users.
WiFi is presently working with 5 GHz and work to clear some more channels in 6 Ghz is where the 802.11ax working group is headed. Eventually WiFi may adopt some higher frequency channels as the demands for more bandwidth in urban areas grows.
802.11ad uses 58-64 GHz which is very hard to work with when it was first established. The problem is that the short range is one problem and propagation through walls is almost impossible. In an open field such as a football fields this type of solution can work.
NEW PHONE APRIL 5, 2020
An associate at Best Buy said a new phone is expected to be available in April 5, 2020. The model is now entry level iPhone and its expected to launch at $399 and up.