If the dialed number is currently on a call, it means that the other party is on a call or has rejected your call.
A telephone is a long-distance communication device that can transmit and receive sounds. As early as the 18th century, the word "telephone" existed in Europe, which was used to refer to a microphone strung with wires (cups strung with wires).
The emergence of the telephone is attributed to Alexander Graham Bell. The principle of early telephones is: the sound of speech is a composite vibration in the air, which can be transmitted to a solid body and passed through electrical pulses to conductive metals. Passed on, Bell applied for a patent for the telephone in March 1876.
Telephone communication is a communication technology that converts sound energy and electrical energy into each other and uses the medium of "electricity" to transmit language. The simplest form for two users to communicate is to connect two telephone sets with a pair of lines.
Smartphone:
With the continuous rapid development of IT technology, the processing capabilities of embedded terminal devices are getting stronger and stronger. At the beginning of the 21st century, a kind of personal data assistant appeared (PDA) telephone "smartphone".
In addition to complete fixed-line phone functions, smart phones usually also have large-capacity business card management functions, incoming and outgoing call management functions, phone harassment prevention functions, enterprise group phone and business card management functions, and auxiliary office functions. Many functions, such as: schedule, notes, calendar, calculator, etc.
Early smart phones had certain information exchange capabilities through dial-up Internet access, and realized the functions of sending text messages and receiving text messages. With the development of fixed-line smart phones in China in the past decade, their processing capabilities have been strengthened, gradually increasing the functions of smart phones.