It is rumored that when John Mitchell suddenly recognized during an attempted phone call that his 400 MHz phone had inherent limitations, he immediately reversed his previous decision and championed the portable cell phone concept. Description Several prototypes were made between 1973 and 1983. The product accepted by the FCC weighed 28 ounces (790 g) and was 10 inches (25 cm) high, not including its flexible "rubber duck" whip antenna. In addition to the typical 12-key telephone keypad, it had nine additional special keys: Rcl (recall) Clr (clear) Snd (send) Sto (store) Fcn (function) End Pwr (power) Lock Vol (volume) It employed some of the technology previously used in the ALOHAnet system, including metal–oxide–semiconductor (MOS) transceiver and modem technology. Variants The DynaTAC 8 Series, Classic, Classic II, Ultra Classic, and Ultra Classic II had an LED display, with red LEDs; the DynaTAC International Series with green LEDs, and the DynaTAC 6000XL used a vacuum fluorescent display. These displays were severely limited in what information they could show. The battery allowed for a call of up to 60 minutes, after which it was necessary to charge the phone up to 10 hours in a trickle charger or one hour in a fast charger, which was a separate accessory. While still retaining the DynaTAC name, the 6000XL was completely unrelated to the DynaTAC 8000 Series, in that it was a transportable phone meant for installation in a vehicle. The 6000XL was later reconfigured as the Motorola Tough Talker, with a ruggedized build intended for construction sites, emergency workers, and special events planners. The DynaTAC Series was succeeded by the MicroTAC Series in 1989. Legacy With the removal of analog network cells nearly all over the world, the DynaTAC models running on AMPS or other analog networks are mostly obsolete. Thus, they are more collectors' items than usable telephones. The International series, however, will still work, but only on GSM 900 cells. The DynaTac 8000X, due to its resemblance in size and weight to a standard clay-fired brick, was nicknamed the brick phone by users, a term later applied to other brands as a contrast to smaller handsets appearing in the 1990s. Portability While it might be considered extremely unwieldy by modern standards, at the time it was considered revolutionary because mobile telephones were bulky affairs installed in vehicles or in heavy briefcases. The DynaTAC 8000X was long and weighed . It was