This excellent photograph shows a Dutch Post Telegraph and Telephone mobile radio. The set was developed in 1937 from PTT specifications and saw use from 1939 onwards. Change-over from receive to transmit is effected by the large lever on the front panel. The transmitter is pre-set on a single frequency while the receiver is tuneable over the frequency range. I do not know if this set actually connected to their public switched telephone network.
More good details are here.
Many people contributed to the walkie talkie, the handie talkie, and portable point to point communications. All, including Gross, contributed greatly. In 1946, the very first circuit boards, a product of war technology, became commercially available. Check out the small board in the lower right hand corner. It would take many years before such boards became common.