1. A character input system, performing communication between a communication terminal and a disambiguation server via a network, and transmitting and specifying character strings or words from the disambiguation server in accordance with a key sequence performed at the portable terminal, the communication terminal comprising number keys from 0 to 9 respectively allocated to a plurality of characters, display means for displaying information, and display control means for displaying a character string or word transmitted from the disambiguation server on the display means, and the disambiguation server comprising a character string database storing candidate character strings or candidate words corresponding to key information strings from the number keys, and information returning means for searching the character string database based on a key information string arriving via the network, and acquiring and returning candidate character strings or candidate words to the communication terminal.