No it isn't, you can use the same settings for imap access via iphones and configure them in either Outlook, Outlook Express, Windows Live Mail Desktop, etc. There are two important things to remember which I'll cover below. Here are the yahoo imap settings that I use in Outlook:
Incoming: imap.mail.yahoo.com - Port 993 - SSL Encryption enabled
Outgoing: smtp.mail.yahoo.co.uk - port 465 - SSL Encryption enabled
Now, important things to remember:
1. User Name: You must use your full Yahoo e-mail address as the user name. You cannot just use your Yahoo ID alone in this box. The reason why Yahoo makes you use your full Yahoo e-mail address is because Yahoo has contracts with several ISP's including AT&T, Frontier, Nokia Mail, etc to manage their e-mail services for them .
2. Inbox storage. It's probably a good idea not to keep over 500 e-mails at a time in your inbox. Doing this causes the Yahoo e-mail server to get fragmented for your account and you will most likely start getting connection errors, which means then that you will have to log on via Yahoo's web mail interface to fix.
3. If you get a "cannot update e-mail headers" error when opening e-mails, just ignore this. All they're really telling you is that Yahoo's mail server will not allow your e-mail program to add it's own headers to the message.
Yes, a Yahoo Mail Plus subscription is still required for POP3 access, however, with people accessing their e-mail accounts in more then just one place or on more then just one device, imap access is still the more popular method because your e-mails don't get deleted from the server immediately like they do with POP3, so you get to decide when they are deleted or when you no longer need them.