Totally. HTTP login is a solved problem, browsers are very good at remembering different identities, it's simple to use, digest authentication is far more secure than a plaintext POST, and it vastly improves the statelessness of the HTTP traffic.

The only real problem is the browser UIs don't provide enough support for HTTP auth. For instance, does your browser tell you when you're authenticated with a site? Does it provide you with a logout button? I'm guessing not.

Yahoo! don't want to by default expose their users' usernames inside the OpenID string (for perhaps-spurious 'privacy' reasons).

You can, at openid.yahoo.com activate my.yahoo.com/myusername, or choose another currently-unused string for the login.

There's an extension to OpenID that Yahoo! are pushing that would let you put just 'yahoo.com' in the OpenID login box.

If the telco knows your handset doesn't support MMS, on receipt of a message you'll typically get an SMS containing a URL to visit to view the message at your leisure.

No idea if that would work with iPhone's Safari - I doubt it as they've mostly been proprietary Flash interfaces from what I've seen.