Why do the XPhone UM services not start (anymore)?

Necessary UM services won't be started altough every setting on the XPhone Server has been set accordingly. 
In the logs you will find the notification that the UMServer can't be reached and the problem itself is a remoting problem.

Open the file UMSCOMClient.dll.config in the program directory of the XPhone Server subfolder "UMS\bin".

Change the following sections

<channels> 
<channel ref="http" port="0"> 

as the following: 

<channels> 
<channel ref="http" port="0" proxyServer="" proxyPort="0"> 

You should be able to start the serves again now.