I think it depends. I know if Iím calling say for help with my utility bill, phone or cable service, something that might take some time, I honestly donít know what time they close. Iíve always figured if they are closed, like many places, I will simply get a recorded message, stating the hours of operation, and plan to call back when theyíre open. If someone answers, again, I have no way of knowing theyíre closing in 2 minutes, or that particular person is supposed to be off in 2 minutes. A lot of places have CS 24/7, so its never really occurred to me I might be an SS by calling and then keeping someone on the phone past closing time. So no, I vote not rude. If someone answers, Iím just assuming they are still open, on the clock, and able to help me with whatever I need.
Now if Iím calling a smaller company, or store, that may have fixed hours, or a business when I know they are only there until x time, I generally will try not to call around the time I think they might be closing. If x store is open until 9, and Iím calling and know they might have to hunt down what Iím looking for, I wonít call at 8:58. Iíll try and call earlier, or the next day.
As for the retail comparisons, I work in retail, and I can't tell you how much I hate when someone meanders in 10-15 minutes before closing, KNOWING what time we close, yet still thinks its ok to take their sweet time trying clothes on. We can't do anything about it, as per corporate, we cannot tell them flat out we are closing and you need to finish up. But in a call center or CS phone atmosphere, as I said, I'd be very surprised if most people calling in actually knew when they closed.