Sprint is reportedly considering a bid for T-Mobile US - a $20 billion deal, according to the Wall Street Journal.
Sprint is said to be studying the regulatory hurdles and could offer a bid for T-Mobile during the first half of 2014.
The companies would have almost 53 million combined post-paid subscribers - the industry's most valuable customers.
That number is still far behind Verizon's 95 million contracted souls and AT&T's 72 million.
Sprint's attempt to make a deal comes after it was acquired by SoftBank Corp earlier this year. Similarly,T-Mobile just completed a merger with smaller US carrier MetroPCS.
It's not clear if the deal would go through US regulators, as a merger of the third and fourth largest carrier in the US could create monopoly fears.
In September, T-Mobile CFO Braxton Carter wasn't opposed to the idea of a merger with Sprint.
"It's the logical ultimate combination," Carter said, when speaking about T-Mobile and Sprint together.
UK-carrier EE was formed in 2010 through the merger of T-Mobile and Orange. It appears something similar could happen in the US.
A Sprint and T-Mobile combination would yield 53 million customers. It would still put the duo at a distant third behind Verizon Wireless, which has about 95 million postpaid subscribers, and AT&T, with about 72 million.