I thought I would run to LiveJournal and post using my newly-working GPRS/Bluetooth setup. It took a few hours to figure out how to get this going, but it's working now and seems like it's going to do well for me. The speed right now seems to be roughly equivalent to dial-up speeds (actually, it feels faster, but that may just be my excitement at the novelty of it). So far I have successfully tested SSH and HTTP with it. The phone is sitting in the kitchen and I'm in the next room over. I'm using T-Mobile service.
I think I probably made a mistake not getting the built-in Bluetooth and wireless card. I bought a pretty stripped-down X40 without that stuff or the "media slice" in order to save some dough. Maybe it's not a mistake; the problem of course with built-in stuff is it becomes outmoded as new protocols come along, and isn't transferrable from machine to machine. I already had a 54g card, and now I have a USB Bluetooth dongle (cost only $40ish). And this dongle may be better than the standard---it did pick up a coworker's phone 3 floors up in our office building today. Crazy stuff. The downside to the dongle is that it sticks out to the side from the USB port a good 2-inches, so using it while sitting on the bus or train is not going to be as practical as I was hoping. But, there is a USB cord, so connecting the dongle via cord while keeping the dongle and the phone in my pocket should work fine if I really want to do that.
Backing up---Debian installation went relatively smoothly, though I did have a couple hours of frustration in making a bootable USB stick (no drives on this machine). In the end, I discovered that the mbr utilities that are recommended in most instruction sets for doing this just don't work (for me). "lilo -M" was what I used in the end to create a working MBR on the stick. After that, everything went well. Next time maybe I will try a netboot install.
ACPI is working. Shut the lid, it goes to sleep, open the lid, it comes back quick. Very happy with that. Just using suspend-to-memory right now. I'm going to look into suspend-to-disk later. There were some tricks to getting this working; maybe I'll write those up later.
Two hardware obstacles yet to overcome. I haven't been able to get IrDA to work yet, and the internal modem seems to be a known problem for which most people are using a proprietary driver. I haven't explored that much yet; it would have come in handy this past weekend in Florida, but now that I have the GPRS working it's much less important.
This Linksys Bluetooth dongle worked out of the box with the bluez-utils. The chatscript and ppp option instructions at http://www.xmission.com/~bmidgley/tmobile/ worked for me almost literally. The init string he uses caused an error on my T610. So I substituted the init string that is included in the Windows driver and script files supplied for the T610 at http://www.sonyericsson.com (FYI: these files are explicitly provided under "no license"). At first I followed his suggestion of specifying nameserver addresses, but that didn't work. Not specifying them did work. There were pieces from a lot of other different sites that led to getting this working as well as some annoying voice time with T-Mobile Customer Care; I should probably spell them out before I forget (if for no other reason than I might have to do it again for myself :) ).
I still miss my Sidekick dearly and have not resolved to sell it quite yet. But this is sure nice. If only the Sidekick had Bluetooth, or even a working USB or IrDA connection. Or if only the Sidekick data service was the same as the Unlimited Internet plan so I could just swap the SIM back and forth..