Americans love them, and hate them. And many say they can\'t imagine living without their mobile phones. A survey released Friday shows the mixed emotions people feel about their devices, with many saying they use the phones to save time, but worry about spending too much time using them. The Pew Internet Project survey found that 67 percent of cell owners find themselves checking their phone for messages, alerts, or calls, even when they don\'t notice their phone ringing or vibrating. It found 44 percent have slept with their phone next to their bed because they wanted to make sure they did not miss important calls or messages, and 29 percent of cell owners describe their phone as \"something they can\'t imagine living without.\" Yet many in the survey also reported the negative impact of being constantly available: 11 percent of mobile phone owners said they worry that they are spending too much time with their phone, and 12 percent said people they know tell them that they are spending too much time using their phone. Additionally, 39 percent of those with mobile phones said they have received complaints because they fail to respond promptly to calls or messages. The survey found 65 percent of cell owners say that their phone has made it a lot easier to stay in touch with the people they care about but nine percent said using the phones makes it harder to disconnect from work life. The survey found some 15 percent of adults do not own a cell phone at all, mostly because they feel they don\'t need one. Just one in five non-adopters say that cost is the main reason. It found 40 percent of adults who own a cell phone have not yet upgraded to a smartphone, with economics being a major factor for one-third of those.