By default, if you sign up with the Comcast initially you will be on POP3, as ios works with IMAP only you need to request an IMAP account from Comcast. Remember, no need to call or to make any kind of paperwork etc. Simply go to the settings or Preferences which you use to access your POP3 account. Choose new account as IMAP. Once you are done just make sure you have started retrieving the old emails. Once you get the old emails into your IMAP profile configured in your iPhone delete the old POP3 profile from your Comcast account. If you still waiting to go through with it, call our 24*7 Comcast Email Support Experts.