Motivation

Phone numbers are often stored in personal address books or contact directories.

Furthermore, they are presented on websites or integrated into the personal footer under emails.
 
By linking your address books to the telephone system via CTI, it is possible to make a call directly from your address books.

Only a standard compliant storage enables a guaranteed reachability of the destination number from all networks (RWTH telephone network, mobile network, international roaming or home network).

Standard-compliant

Always write phone numbers in FQTN (Fully Qualified Telephone Number) according to the ITU-T standard E.164. 

This has the advantage that the number is always unique.
This means that the telephone number can be uniquely addressed by every telephone system and every telephone service provider. 

Examples