For the First Time in Pakistan Ufone offers you a collect call service. With Ufone Collect Call you can remain connected and make calls even when you don’t wish to pay for a call, so you no longer require to send people missed calls as the receiving party pays for the call charges.
It provides you the convenience of calling even when your account balance does not allow you to make a call on the Ufone network.
This service is ideal for Users who run out of balance, that wish the other party to pay the charges in a business-related call or children who wish to call their parents and not want to pay for the call charges. In order to initiate a Ufone Collect Call request, simply dial 11 followed by the desired Ufone number. e.g. 1103335199942 . If the other party accepts your collect call your call will be connected right away. However If the dialed number does not have sufficient balance or cancels your request you will receive a SMS notification.
However, there is a way to block this calls too. There are methods to block calls in Source