Sprint and T-Mobile are raising $10 billion to jointly bid in the upcoming 600 MHz incentive auctions, according to the Wall Street Journal.

This follows an earlier Bloomberg report saying Sprint and T-Mobile are planning a joint venture, to be run by T-Mobile, for bidding in the auction. The $10 billion for spectrum is reportedly part of the $45 billion SoftBank is rounding up from lenders.

The Journal’s sources indicated that the joint venture is only one of the ideas being considered and that it and other terms of the deal could change. The companies could announce the transaction later this summer.

But besides a lengthy review from skeptical U.S. regulators, the companies might face changes in auction rules. The FCC currently has set aside 600 MHz spectrum in each market that bidders with large below 1-GHz holdings—namely AT&T and Verizon—won’t be allowed to bid on. However, should the competitive landscape change due to carrier consolidation, the FCC has the right to change the rules.

Aside from rules favoring smaller carriers, Sprint and T-Mobile could have a financial advantage in the auctions. As the report points out, the rumored $10 billion for the JV would outdo the $9 billion AT&T has set aside for the incentive auctions.