Sprint (S) overhauls its prices and provides lifetime unlimited voice/data guarantees just a day after the SoftBank (SFTBF.PK) merger closed. The carrier is offering smartphone users unlimited voice/text/data for $80/month for the first line on an account, with the price gradually dropping for lines 2-4. A $110/month plan that throws in 5GB of hotspot usage is also being rolled out. SoftBank CEO Masayoshi Son has made it clear Sprint will compete aggressively on price against AT&T (T) and Verizon (VZ), who have been trying to migrate subs to costly shared data plans. Sprint's announcement shortly follows the launch of T-Mobile's (TMUS) Jump smartphone upgrade plan.