Bluejacking

Bluejacking
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. So, personalised messages like 'I like your pink top' and the startled expressions that result is where the fun really starts.

Explanation;
1. Get your hands on a Bluetooth-enabled device mobile phone.
2. Create a new phone book contact, with the message you want to send to someone in the 'Name' field. e.g. 'I like the look of your cappuccino'
3. Go to a busy place (Busy shopping centre, High Street, On a train/ tube / bus, Cinema, Cafe/ restaurant/ pub, Mobile phone shop, Electronics shop, etc..)
4. Select the contact you made earlier, and choose 'Send via Bluetooth'
5. Your phone will search for other Bluetooth devices roughly 10 metres around you. It will either list available devices, or say none could be found. If it doesn't find any, choose another spot.
6. Your phone will list the names of devices in range. Sometimes the names will give you a clue to the model of phone.
7. Select one of these devices listed for your phone book contact to be sent to.
8. If all goes well, your contact will be sent to the selected device
9. If you can, try to casually look around you and see if you spot anybody with a bluetooth enabled phone/device nearby looking truly puzzled. It would help greatly if you know which phones have Bluetooth and which don't. This way, you can eliminate anybody who is looking at, say, their Nokia 3310 which doesn't have Bluetooth.
10. The rest, as they say, is up to you.
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In case it all goes wrong:
If you manage to identify your victim and they are looking angry rather than puzzled & confused, jellyellie's advise is to run, not walk, in the opposite direction!
The Reveal:
'The Reveal' is what it all comes down to in the end. It is what your messages have been building up to, and it's certainly the climax of your exchange.
If you know who your victim is, when it's time for you to leave the area send them a contact saying something like ''Listen out for 'parrot''. Then, as you walk past them, say (loudly) to yourself ''I hope my parrot will be OK!'' That will definitely get their attention.