A missed call is a telephone call that is deliberately terminated by the caller before being answered by its intended recipient, in order to communicate a pre-agreed message without paying the cost of a call. For example, a group of friends may agree that two missed calls in succession means "I am running late". The practice is common in South Asia, the Philippines and Africa.
Unlimited talk is not available in some parts of the world
It cost to answer a call in in parts of South Asia, the Philippines and Africa therefore this is not an unlimited talk plan where the person is charged for a period of time not matter how many calls are made but  rather they are charge for each call.  
( z1 available :polarity - :ARG2 ( z2 talk :mod ( z3 unlimited ) ) :location ( z4 part :mod ( z5 some ) :part-of ( z6 world ) ) )