Merger might be bad then.
Same as when Sprint bought Nextel and killed it
But, without merger, Sprint may die, leaving only 3, leading to price increases.
If Sprint goes bankrupt another company buys out its network and customer base and continues running it. (With a clean balance sheet, so they can actually afford to be price aggressive.)
The network doesn't get shut down and customer shut off in case of bankruptcy. So that is no reason to oppose a Sprint-TMO merger.
Sprint can merge with whomever. Just as long as it is not tmobile. Lol