Verify that the device is set to show a sufficient number of messages, and don't keep more messages in the mailbox than can be downloaded by the device.

/Rolf 

Using the iphone, some messages are not picked up by the iphone

the setup is using pop email

not sure but it seems to work with att as a carrier but more of an issue on Verizon

I don't have a suggestion on your particular problem but do have several users with Blackberrys, iPhones and/or iPads.  For those who want mail delivered in real time I use a Forward file to forward all messages to their Verizon or Blackberry address (no AT&T users).  The others access email via IMAP.