The iphone is using data while on standby.
My 50MB of gprs are being used without any application open.

Is it the same on android? As i heard the BB is the only device that doesn't ping the server all the time due to pin and push technology.
What i do is turn data on when i need it but it's frustrating as i want to keep whatsapp online all the time.
On Android you can switch off background sync and etc.
Apple has their own push technology, i guess it uses bandwidth always. But how much - noone knows...
But without switching off anything...does Android consume data? (no running application- 4 to 5 MB a day)
ehmm I dont think so ... I have Gprs turned on all day, and it almosts lasts me a month if I only use whatsapp and gtalk ..

Edit: On an Android ofc **
configure your mail & account settings to use push and disable manual/scheduled fetch
Configure the Sync of some applications to once per [a big amount of time], especially gmail, email, twitter etc.

When the push mode is enabled apps consume usually 5 to 10 times less bandwidth, on android

I suggest you to remove Skype if you have it :)
I removed all email accounts and i never browse the net.

50MB is not getting me to the end of the month for only whatsapp, and by switching off data all the time i don't need it.

What i want is to keep whatsapp online with that quota