Some time ago I switched my calendar to
30Boxes and have been using it ever since. It works great for me. 30Boxes made the race against Yahoo Calendar and it looks like I am going to stick with it. Now
30Boxes Mobile has been announced last week and I installed it on my Nokia 9300. After using it for a day with GPRS it confirms what I have seen with practically all mobile wireless web applications so far. They are very slow (to the point of not being practically usable anymore), overall program usability is a pain in the neck having to use the tab button or the cursor like a disk jockey dozen times before seeing or doing anything meaningful.
In short, unless you really have no other way of accessing the Internet with your laptop or from a desk PC, using wireless Internet web access from your mobile phone remains a pain in the neck. To me it is still a miracle how someone like, e.g. Opera, can make a living with licensing products to such a market. I can only assume that they have been lucky so far because most of their customers are probably not using it themself in business but just need a browser on their mobile phones pre-installed by default. Let's hope for them (Opera) and others that this all changes soon before cost-conscious buyers within Nokia and others might notice it too and take it off from their BOMs...
Now back to 30Boxes. I continue (as mentioned) to use it on my laptop but unless lightning strikes that machine I won't use it on my mobile phone.