Warrants have legal meaning but little practical impact. They can be requested and granted very easily. The process offers very little protection. If the cops ask for warrant to request the list of numbers called, they will get it.

That said, warrants are not always needed. The logic goes that the phone company already knows who you have called. They needed that information when they connected the calls. They store that information for billing purposes. So connection/metadata isn't private because you have already shared it with the phone company. In many countries that is sufficient to moot the entire warrant debate. (This logic then extends to other data used to make connections and route internet traffic such as IP addresses.) And if the phone company/ISP is a state-owned/backed/licensed enterprise there is little privacy left to argue over.