Burlington speech-recognition software maker Nuance Communications Inc. tumbled after first-quarter earnings and revenue trailed estimates on deferred sales in its mobile segment. Nuance said earnings excluding some items, reached 34 cents a share, compared to estimates of 36 cents. The company in December agreed to acquire Vlingo Inc. to gain a system that conducts Internet searches based on voice commands in a bid to capture growing demand for voice-command technology. Nuance said “more comprehensive and complex’’ relationships with mobile customers caused revenue deferral during its fiscal first quarter.