Forward on busy and in the answer more than an extension

[Peu]

hello,
good night,

I have a client that wants the solution, he has 4 analog. extensions with voice mail.
extensions 2010, 2011, 2012 and 2013.

sample;

incoming for the extension 2010 is busy or in the answer Forwarding for 2011 is busy or in the answer, 2013 are busy or in the answer, voice mail 2010.
incoming for the extension 2011 is busy or in the answer Forwarding for 2010 is busy or in the answer, 2013 are busy or in the answer, voice mail 2011.
incoming for the extension 2012 is busy or in the answer Forwarding for 2011 is busy or in the answer, 2013 are busy or in the answer, voice mail 2012.
incoming for the extension 2013 is busy or in the answer Forwarding for 2011 is busy or in the answer, 2012 are busy or in the answer, voice mail 2010.

in the enterprise, OTUC it is possible or other aplication?

excuses my English
thank you