Methods, devices and computer-readable mediums providing chat service

A method of providing a chat service between a first device and a plurality of second devices, the method comprising:

• creating a first chat room to display first visual signs transmitted between the first device and the plurality of second devices;
• receiving a command to select one or more of the plurality of second devices while the first chat room is displayed on the first device;
• selecting the one or more of the plurality of second devices based on the command;
• creating a second chat room to display second visual signs transmitted between the first device and the selected one or more of the plurality of second devices;
• merging only a subset of the second visual signs displayed in the second chat room with the first visual signs displayed in the first chat room;
• and
• displaying, in sequence, the merged visual signs in the first chat room based on transmission or reception times of the merged visual signs, wherein
• the merging and the displaying are based on permission received from at least one of the selected one or more of the plurality of second devices,
• the subset of the -second visual signs includes a first portion of the second visual signs for which the permission is received and does not include a second portion of the second visual signs for which the permission is not received,
• the subset of the second visual signs includes only second visual signs permitted by the at least one of the selected one or more of the plurality of second devices to be merged with the first visual signs displayed in the first chat room, and
• the subset of the second visual signs includes less than all of the second visual signs displayed in the second chat room.