Hmm... Sounds very odd. Do you have a data tracking app on your phone, do you see the total rising? Go to Settings, Accounts & Sync, then turn off Auto sync first, check, then turn off background data later. If you load an app like Norton Mobile Utilities you can monitor which app is using up network traffic (Home, Device, then tap the Network Graph). However you'll have to do this several times to see the relative difference?

 

Also if you check your battery monitor, it will tell you what software is consuming your battery.

 

My phone (Samsung Galaxy S2) is having exactly the same problem!...

Although I updated to 2.3.6 a little while ago (a week ago or so), the auto sending started just today (or last night - 31st Dec). It seemed to coincide with using my phone as a Wifi hotspot for my laptop. ....first thought is of course that it has a virus of sorts??

To explain the problem:
The phone is in 'locked' state. All of a sudden (every 10-15mins or so) the phone will un-lock itself (in the way it does when 'swiping' the screen to un-lock it), then a 'Sending...' message is displayed at the bottom of the screen, and then it locks itself again. As if I had pressed the power button on the right side of the phone.

Very weird and somewhat concerning. If anyone can shed any light on it, that would be great

Is there an app someone could suggest (if it exists) to monitor phone use of outgoing data/messages? I really don't know what it's sending, if anything?

 

3G watchdog from the market is a good way of seeing what data is being used on your s2. very good app.