Well, Posterous seems to be winning the "which blog should Del use" battle here, although none of the three I'm playing with are working 100% as I'd like.
Starting with an existing theme and tweaking I ended up with a better looking one here than I did at tumblr. Wordpress won't let me tweak a them without paying them. That's not a deal breaker because I'm cheap (though I am), it's just that if I'm gonna pay for it then I might as well keep on using the installed WP on my own friggin webserver.
A test email from the ol' telephone showed up just fine here at Posterous. It's been 15 minutes and two test emails and still my test posts haven't showed up on tumblr. Haven't tried email posting on WP yet 'cause I haven't set it up to do that yet. Given that Posterous intends for posts to be emailed by default that makes Posterous the winner here. (update: just checked, now tumblr is showing the 2nd test post from gmail, but still nothing sent from the phone...)
Unfortunately none of them load great in the mini Opera on my phone. The tumblr site is all over the place with overlapping images and crap making it difficult to log in, while my site loads the full-but-zoomed-out full page. Specifying "/mobile" on the end of my URL loads a mobile page that only shows the latest post, with plain black text on a plain white background (ugly). WP loads a mobile ("touch" it says) version of my site quite nicely, but the main site just renders blank white so I can't log in to the dashboard. Loading m.wp works okay, but still tries to load the full dashboard in some cases which taxes the phone pretty bad. Posterous loads a decent mobile version of my site by default, but the main dashboard thing is still full-size and zoomed out. At least the Posterous one loads though. Advantage Posterous I guess.
Of course this will all change if I ever get a new, decent phone. Or maybe christmas will bring that iPod touch I asked for.