iPhone is Locking POP3 Account

This is normal behavior of a pop account. The iphone is a full-functioning email client much like Outlook and Mac Mail.

That being said, POP3 is designed to be accessed by ONLY 1 device at a time. Since your computer and iPhone are vying for the same message, the account locks one out. The only way to get around this is to find an IMAP server where this issue does not occur.

Cheers!

The iPhone is not putting a lock on the incoming mail server. The iPhone's Mail client may be holding the communication with the incoming mail server to long after the incoming mail server has been checked for new messages and/or after downloading new messages received at the incoming mail mail server, but it isn't the iPhone that is putting a lock on the incoming mail server. The incoming mail server is doing the lock. Although it is possible to access a POP account with more than one email client, a POP account is designed to be accessed with a single email client only. One email client at a time can check the incoming mail server for new messages, and/or download new messages received at the incoming mail server. If a 2nd email client attempts to do this while another email client is doing the same, the incoming mail server will temporarily lock out the 2nd email client since only one email client at a time can communicate with the incoming mail server with a POP account.

Not a problem with an IMAP account.

What other device have you used to retrieve mail? If it was a Blackberry, a Blackberry does not communicate direct with the incoming mail serve for any email account as does the iPhone's Mail client.

As I included with my previous post, a Blackberry does not communicate direct with the incoming mail server with any email account. RIM has a dedicated email delivery service for the Blackberry, which is located in Canada. This provides Push access for received messages with all accounts regardless the account type including with a POP account that is not supported otherwise.

The iPhone's Mail application communicates direct with the incoming mail server for an email account no different from the Mail.app on your Mac or with any email client used to access an email account on any computer.

That is great, but you kept comparing this to a Blackberry which is no comparison, and now switching to something else.

Downloading new messages with Outlook followed by downloading new messages with Entourage IS NOT the same as doing this with both email clients AT THE SAME TIME.

The iPhone's Mail client may not be closing communication with the incoming mail server fast enough but this does not change the fact that two email clients cannot check the incoming mail server for new messages with a POP account and/or download new messages at the same time. This is a POP account limitation with POP account access from the early dark ages of email account access with a computer which is not a problem with an IMAP account. A POP account is designed to be accessed with a single email client only. An IMAP account is specifically designed to be accessed with more than one email client.

It is great that you acknowledge these things you apparently were not aware of before and that you have submitted a suggestion to Apple. I have an IMAP account so no such problem along with all server stored mailboxes available and kept synchronized with the server automatically with each email client used to access the account which is not available with a POP account which is designed to be accessed with a single email client only. FYI - the future is with cloud computing, which an IMAP account has included since it has been available.

I have a BT internet email account which is a POP account. I don't want to go to the trouble of changing my email address. So I suppose there is no way to change to an IMAP email account without doing that, is there.

Not unless the email account provider for the account supports accessing the account as a POP or IMAP account. This is up to the email account provider for the account, and most internet service providers support POP account account access only.

If BT Internet supports accessing the account as an IMAP account, yes. If not and you want IMAP account access, you need to switch to an email account provider that supports IMAP account access.