BlueJacking
First up, you need to know what Bluetooth is. There are lots of types of modern devices that incorporate Bluetooth as one of their many features. PDAs, mobile phones and laptops are a few of these modern devices. Bluetooth means that Bluetooth enabled devices can send things like phonebook/address book contacts, pictures & notes to other Bluetooth enabled devices wirelessly over a range of about 10 metres. So, we've got past the boring part. Now, using a phone with Bluetooth, you can create a phonebook contact and write a message, eg. 'Hello, you've been bluejacked', in the 'Name' field. Then you can search for other phones with Bluetooth and send that phonebook contact to them. On their phone, a message will popup saying "'Hello, you've been bluejacked' has just been received by Bluetooth" or something along those lines. For most 'victims' they will have no idea as to how the message appeared on their phone.