Research Proves Mobile Phones and Sleep Do Go Together, astudy conducted by Swinburne's Brain Sciences Institute examined the impact of mobile phone use immediately before bedtime on the brain and sleep patterns:

The quality of sleep for Australia's 12 million mobile phone users is not affected by calls on mobiles before bedtime, according to the world's largest independent study into mobile phones and sleep quality. Although the results showed there were differences in the brain's electrical activity in the initial part of sleep as a result of using a mobile before bedtime, this had no affect on sleep variables such as the time it takes to get to sleep, the length of time asleep or whether the person slept lightly or deeply and therefore does not affect the overall quality of a person's sleep. (...)

PhD student, Sarah Loughran, undertook the study and said the results indicate that using a mobile phone before going to sleep does not appear to influence whether a person has a good night's sleep. (...) The study confirms the results of a previous study carried out in Switzerland involving a smaller number of participants.