If you have recently “hacktivated” your iPhone, which means activating it to work with carriers other than the official ones, you may have encountered push notification issues. In most cases, push notifications don’t work properly or even don’t work at all.
There is a simple fix for this and it’s called Push Doctor. Simply add the following source to Cydia then look for Push Doctor: http://www.cmdshft.ipwn.me/apt/
After installing Push Doctor, reboot your iPhone.
Push Doctor works very well with 3.1.3 and 3.1.2. It is free and has the support of the Dev Team, so you can go with it safely.