The CS410 is an ISDN phone which is working with every S0 Bus working with Euro-ISDN (DSS1).
The CS410–U is an Up0 phone which is working at an Up0 Bus of an elmeg PBX.
CS400xt | CS410 | CS410-U
CS410 | CS410-U
 Differences between CS410 and CS410-U
 DECT Headsets
Differences between CS410 and CS410-U