WordPress Mobile Admin allows you to blog from your mobile.
Head over to Wapple and fill out the simple form, you should be able to get your dev key within a couple of minutes!
Have you entered your dev key into the Wapple Architect settings? If not, head over to Settings > Wapple Architect (or Options > Wapple Architect if you're on version 2.3.3 and under) and enter it into the "Dev Key" input box.
In older versions of the plugin, you needed SOAP and SimpleXML, but not any more! From version 2.0, the dependancy on SimpleXML has been totally removed! You also do not need SOAP and can communicate with Wapple's web services via REST.
On some handsets on certain networks, file uploading doesn't work. Even though the mobile phone supports it, it doesn't like it. If you find you're having problems with posting, head to "Dashboard", then "Profile" and turn it off for your user.