Here is what I had to do to get my pop email account working with my iPhone,
1) Log into my-tmobile
here
2) Go to connect and share and click on configure email.
3) Add your email account into your My Tmobile email accounts (If you already have your email account working on outlook or outlook express, My Tmobile will give you the option to download their software that will automatically import your settings)
4) On your iPhone, add the email address and password.
5) you can use your regular incoming mail server.
6) for outgoing mail, use the following settings:
server: on
Host Name: myemail.t-mobile.com
user name: your 10 digit phone number and a colon followed by 1
(ie: 2125559999:1)
Password: The same password you use to access your email
SSL: off
authentication: password
Server port: 587
This is how I was finally able to get my iphone to send emails using my work email. It should work for you as well, but obviously I cant make any promises. I spent a ridiculous amount of time until I finally figured this out. Hopefully this will save you all time.