I am not a lawyer but here it goes:

If the target of the warrant itself is the carrier/telecom - probably constitutional, but I imagine there'd need to be a pretty good explanation.

If the target of the warrant itself is a single customer of the carrier/telecom - Absolutely unconstitutional.

E.g. You can't get the transaction history of every customer of a bank just because one of its customers is a suspect.

(Edited for clarity.)