I am a IELTS learner.
I am wondering about this sentence:
Please call free on 777-777-7777
It means "call me anytime you want"?
Or "you are not charged for the call on the number"?
"Call-free" means without charge. A business can set up a phone number that allows customers to call them for free. The business pays the cost of the calls. These are sometimes called free-phone or toll-free numbers. In the USA many such number start 1-800, 877, 866, 855, 844 or 833. In the UK, free-phone numbers start 0800 or 0808
To give the meaning "you can call me any time" you could say "feel free to call me"
The ambiguity in the different meanings of "free" causes problems even for native speakers, though this particular example is quite clear.