Back in the 1990's I worked with an interconnect that paid $50 for the week you were on call and time spent on emergency service calls. The problem is the company would service any system whether they knew it or not: All the variations of Nortel, AT&T, Comdial, Iwatsu, TIE, Panasonic, Inter-Tel, NEC, Macro-Tel, Sun-Moon-Star, Nitsuko, Norstar, Nortel, Samsung, Toshiba...you get the idea.
Kind of like a hooker, anywhere anytime as long as you say you have money. (pager days, no cell phones)
Biggest problem is they kept hiring workers that would say "I'm only certified on Nitsuko. I don't know anything else so I can be on call" So out of 8 tech's and a "supervisor" tech, only the supervisor tech and myself were the only ones on call. Until the company decided that he lived too far away (30 miles) from our local service area. You can see where this is going. A couple times they did have an extra tech that was willing to be on call
On Fridays when the office forwarded the phones to the Answering Service they were suppose to tell them who the on call tech was...oops always forgot. I would be on call for months at a time.
SIDE NOTE: I had accumulated too much vacation time and the company demanded I started taking time off. My wife worked Tuesdays through Fridays so I let the company know that I would be taking every Monday off. After the first week they informed me that I was not allowed to do that because they needed me.
When I quit they had to pay me for my 168 hours accumulated vacation pay.
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