Iphone won't work well with SBC global

I activated my phone yesterday. Every since, my macbook and iphone are having trouble accepting email. It continues to tell me "password rejected." When i send email it goes through fast sometimes and just sits in the outbox other times. But it seems to be worse when retrieving email. I send myself a test message and when i try to retrieve it on my macbook it spins and spins and spins. My IPhone is now a little better as the Apple store changed the settings and I now have Push. My macbook never had this problem until i activated the phone. I am about to return the phone. Somebody help.