I have a few old TM modems in my store room collecting dust. What's the best practice for getting rid of these devices? Recycle bin?

just keep it. you will need to return it when you terminate the line

I thought so too, but I've switched to Maxis already.

Throw it away, or if you want, you can return it to them, but I think they will just recycle it.

What if my original TM modem is faulty and threw away long time ago?

I'll terminate as soon as TIME is available.

Give it away to someone in need. Maybe somebody terminated their service and have to return their modem then it got lost while moving house and now need to pay penalty.

check the specs of these modems and compatibility with openWRT, if cant then recycle , can get a few RM from doing so too. The power supply can be reused, its typically a standard voltage with 1-2A which is not bad.

At one point i had way too many old TM stuff, old modem, old router, old hypptv box, all recycled except for router as that has username and password, so would just install a custom minimal openwrt build on it.

Could also give it to someone in need as mentioned above.

Modem is owned by TM, when faulty they'll replace it so spare on only works for temporary use, really not needed to keep as engineer can come and replace it within a week if ever modem became faulty. Old modem will not support the new turbo speeds.

What kind of modem, streamyx modem or UniFi BTU? If streamyx modem then it's of no use unless you can give to someone who are still on Streamyx. As for UniFi BTU you can return to TM. If you're talking bout router, either recycle it or give to someone in need.