I can sign into mine via my phone using plain old Pocket IE on Windows Mobile 5.
The Solpart menu works by putting submenus on extra lines when you click on a tab. Ugly, but it works.
But once you're in, lots of the fancier bit of course dont' work. The FCK editor doesn't work, but it does show the plain text box instead so you can still type. Action menus don't seem to work, but that may be because mine are all using the DNNMenu instead of Solpart.
Overall the portals I have are just too heavy for mobile use. I'd like to see something that slips in an httpmodule that would detect a mobile browser and then redirect to a special tab where I would place modules designed specifically fto fit. The most useful thing would be to display items from Ventrian's News Articles, or possibly the core blog, at a pinch maybe some forum content, or if nothing else then just plain RSS gathered from around the site would do.
Some third parties have done occasional apps that run in the phone and interact with DNN directly, rather than via a browser. Those have a lot of promise if integrated with a powerful server-side module. I told the last person who asked this to go and ask Chris at Onyaktech.com about mobile support. He is very keen on it and it would be very powerful when combined with his form creator and project management modules. Having direct access via a mobile app to his modules would be enough for all kinds of sales force applications. He currently has a dashboard sort of app for viewing bits and pieces, but it needs more. The more people hassle him the more likely it will happen.
Someone else has posted recently asking for interest in another variation on mobile content delivery.. the post might have been in annoucements or in chat about it here.
There's a mobile app on Snowcovered that shows you portal registrations and other bits.. sort of like a mobile version of the who's online module.
Thats about it from me,.
Rob