A Subversion client on my tablet Asus Transformer?
It looks like there's been a little work porting SVNKit to Android (see this), but actual source code isn't sitting around for anyone to use yet.

It's a little bit incredibly gross, but you could try introducing another syncing setup.  Something like Dropbox to store and sync files on your phone, and then commit the changes when you get to a machine with an SVN client.  This is obviously less than ideal.