Cannot retrieve text or mms messages

my phone simply will not receive messages out of its inbox. when you click on inbox it takes you back to the previous window, either main screen or if you select messages through menu, it takes you back to main menu. my friend has one as well which she purchased around the same time, and it does the same thing. does anyone else have this problem? Why i can't retrieve my MMS when someone sends me? I am sad because it has been twice that I could not retrieve them. I contacted my network operator and the customer service told me that my network is OK.. So, I think there is something wrong with my phone... Please help>!