Son notes SoftBank used aggressive pricing and marketing to gain Japanese mobile share following the acquisition of Vodafone's struggling Japanese unit - "We had nothing we could be proud of ... But we were still able to win more net users than anyone else." - and mentions Sprint is testing new service plans (previous).
T-Mobile, of course, is already quite aggressive with its pricing, and AT&T had made sizable price cuts of its own in response. Verizon is refusing to return fire for now.
Sprint is now down 23% since reports emerged it's giving up on trying to buy T-Mobile for the time being.