Some have their go-to spots. Others will try to do it anywhere. And many prepare themselves for an abrupt ending, even if they make an immediate connection with someone. Kendall Square in Cambridge is the region’s high-tech hub, but it can be a tough place to use some of that technology. Cellphone users say dropped calls are normal, reception can be spotty, and sending an e-mail by phone depends on luck. The inconsistent service is mostly an annoyance for visitors and passersby, but it’s a serious problem for others, especially young start-up entrepreneurs who use their smartphones as virtual offices.