Is there a general guideline about how long a phone system should last???

I know that there are alot of variables, such as quality of installation and type of environment, but where systems made in the early 90's designed to only last a certain amount of years???

The reason for this question is that I am working with a company that called me a few days ago, with a Partner and a VS 4.1 vm. The secretary told me that it was there when she was hired and she is with the company 5 years.

Well anyway, the vm konked out, dead as door nail...and they also told me the system keeps dropping calls and phones go dead and then back up...

Is it unique that a partner system that I would imagine is not more then 7 years old be ready for the scrap pile????

I still see TIE Ultracom's still working and that was the first system I installed when I was a newby...back in '82....

Would like to hear some feedback on the life of phone systems......