Is it permissible for a relative who works in repairing public telephones to take and use a phone card found stuck inside the device?

If a card is found in a public phone, it falls under the ruling of a Luqatah (found item). If it contains credit that has value, and people of average means would care about it, then it must be announced. If its owner comes forward, it should be given to him. Otherwise, one may take possession of it, and its value should be paid to the owner if he eventually appears. However, if the card has no valuable credit, there is no harm in taking possession of it and benefiting from it without any guarantee. And if many cards, each individually of no value, are collected and their total value becomes significant, there is no objection to taking them and benefiting from them, because their dispersal indicates that they belong to different owners.