Combes shocked investors by telling them 189,000 of its phone connections were canceled in the first three months of the year, the sharpest decline since 2015.

Struggling Sprint and T-Mobile have been waiting for regulatory approval to finalize their $26 billion merger. Combes told investors if the merger didn't go through, both companies would not be an effective nationwide telecom.

Sprint said in a regulatory filing Tuesday that it suffered a net loss of 189,000 connections during 1Q19 after adding 606,000 during the prior year.

The carrier warned investors: "Sprint is not on a sustainable competitive path."

Sprint's postpaid phone churn, a measure of its ability to keep customers, crept up to 1.82% during 1Q19, from 1.68% during the same period a year ago. Combes explained the YoY increase is due to promotional offers expiring for smartphones.