Iphone 4 Push Mail issues (Gmail)

I just switched from BB 9700 to Iphone 4. Mail has been setup under Mail for Exchange using the m.google.com server. Sometimes, especially when in standby mode I dont get the pushed emails into my phone, however it turns up almost instantly on my BB. Any ideas guys...this is really frustrating and I cant wait to get rid of my BB....

PLS HELP