Abstract: Device for connecting one out of a plurality of internal lines (34,36) to an information exchange subscriber line, such as a telephone, facsimile or telex line, provided with decoding means (28,1-16) to detect dialling disc pulses (a), preferably on base of the time period between edges (b',b") of these pulses, timing means (9,10,12) to determine a time interval after an edge in which the next edge should occur and a test means (13) to ascertain whether said next edge occurred indeed in said interval.