Why won't my gmail push emails to my phone?

[audiokeeffe]

I recently bought an iPhone 4s and I set up my gmail account. I set it up through microsoft exchange, rather than using the gmail icon, because I heard that microsoft exchange pushes emails to the phone instantly. My problem is that it's not pushing emails. Sometimes it does, but most of the time, it only comes through when I go into "mail" and then it 'updates'. I have the settings set to 'push', but it just doesn't seem to be happening that often...what's the problem here?