The T610 has three ways of transferring photos: through email, using Bluetooth, and using infrared. My powerbook doesn't have Bluetooth, so that leaves email and infrared.
Emailing pictures is pretty easy and works fine, but it probably costs money, so a free alternative would be preferred.
So, infrared. I turned on IrDA on my laptop and infrared on the cell phone and was able to make a connection (both said they were connected), but wasn't able to figure out how to do anything with the connection. After trying a bunch of different things I decided that this was a red herring.
I did eventually find some software that allowed me to beam photos from my phone to my powerbook. Unfortunately it only runs in Mac OS 8.6 through 9.x (it can't be installed or run in classic mode on Mac OS X), but it does work.
Strangely the software isn't actually designed for use with the Sony Ericsson T610; instead it's supposed to be used with the C-Pen, a digital pen. The software is available from C-Pen's website (here's a direct link; you'll probably have to right-click on it and download it, as otherwise I just got a web page full of garbage.
Once you've downloaded it, rebooted into Mac OS 9, and installed and started up the program (the one you want is "C Beam"), go to your T610, select the picture you want to send, and go to 'Send'->'Via Infrared'. Then line up the infrared ports of the phone and the Mac and the file should be sent across. Repeat for each picture. (There doesn't appear to be a 'bulk send' operation.)
So, kind of inconvenient, but free and it works. I hope this is of use to someone!