T-Mobile US Inc. and Sprint Corp., fighting to win regulatory clearance for their $26.5 billion merger, are considering possible concessions to salvage the deal, according to people familiar with the situation.

Among the top options being discussed is the separation and potential sale of their so-called prepaid businesses, said the people, who asked not to be identified because the deliberations are private. Other options -- such as selling airwave licenses or setting up a new fourth carrier through a network-leasing...