g-brief in LaTeX and “\Telefon already defined” problem

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g-brief is a document class for LaTeX to write German standard letters. I like this document class very much and prefer it much over the Microsoft Word letter templates.
   LaTeX Error: Command \Telefon already defined.
There is a simple solutions to resolve this error. You can just patch the package. Somewhere below the LaTeX directory you should find the marvosym.sty file. Open this file with a text editor of your choice an search for a line like this:
   \newcommand\Telefon{\mvchr{84}}
There you can change the name of the command \Telefon to something like \Telefonsymbol or the even better way (but I did not test this one): replace \newcommand with \def and leave Telefon as it is.
Another g-brief tip: you can define the following three elements on your document to turn on these various features:
\fenstermarken \faltmarken \trennlinien