'OK' is NOT a reasonable replacement for 'Thank you'.
Neither is hanging up.
If someone does you the favour of helping you out or giving you information on the phone, remember your manners and say 'thank you'. For that matter, remember to say 'please' when you make a request - no 'please' sounds like a demand, and do you really think I'll go out of my way to help you when you can't be respectful to me?
OK. Rant done. I'm tucking the soapbox back in its corner.
Consider this a reminder to mind your manners from Vancouver.