Depending on the design of the printer, that might not be a good idea.

HP laser printers (and for all I know, many others) provide more than toner in their toner cartridges. You get a new drum, new seals, new doctor blade, new developer, and new high-quality toner.

OEM toner cartridges have a designed service life equal to a little bit more than the quantity of toner inside. You can refill them, but you are using a worn-out drum, risking damage (sometimes irreparable) to the printer itself if a seal fails and dumps all the toner into the guts of the printer. It is not uncommon for an aftermarket "rebuilt" toner kit (rebuilt=refilled) to fail in that fashion at its first use because it was not assembled correctly.

In my experience, refilled toner cartridges rarely give print quality as good as a new OEM cartridge, due to worn-out drum and generally inferior quality toner. This is especially true with color laser printers, but even black and white printers show quality degradation.

I just grit my teeth and pay the exorbitant prices for new HP cartridges. I don't print so much that this is too terribly painful, probably only six to ten thousand pages per year. No, wait, a lot less than that. I've printed 10,705 pages in 42 months. In that time, I've gone through all the starter cartridges, then replaced each of the "full" cartridges once, and I think the black one twice. My ratio of color pages to B&W is 2.5 to 1. Assuming about $100 per replacement cartridge, that makes my overall cost about 4.6 cents per page. Not the cheapest printer to run, but not exorbitant either, especially compared to a color inkjet printer. I have been very satisfied with the quality of the output. I've never had an issue with paper curling, and since replacing the pickup/separation rollers, the document feeder has been bullet-proof, even while duplexing.

I was a bit disappointed that I had to spend $40 to replace the pickup and separation rollers after only 10,000 pages, and most of the innards of the printer seem to be made out of plastic, so I suspect that HPs 40,000 page per month duty cycle is a bit, uhhh, optimistic. Of course their recommended monthly page volume is only 2,000 pages.

tanstaafl.

edit: Oh, one more thing... If you dig deeply enough into the printer's menu structure, you can disable the "toner empty" flag and continue printing well past HP's conservative estimate of when the toner cartridge needs replacement. In my experience, I get about 30% more use from the "empty" cartridge.