Stocks jumped in midday trading Monday on corporate dealmaking and easing worries about Japan’s nuclear crisis.

AT&T Inc. said it would buy rival T-Mobile USA for $39 billion, creating the largest U.S. cellphone company, and Charles Schwab Corp. said it would buy online brokerage services provider OptionsXpress for $1 billion. The deals raised hopes that more corporate buyouts could be on the way as businesses become more confident in the economic recovery.