As I discovered while trying it out with my brother and his girlfriend. Bump me! Hey, didn't work. Bump me harder. Don't worry, my phone can take it.

I also have Flash Your QR on my phone, to this end.

And, says Google, there is some effort to standardize contents, including MECARD (vCard but shorter markup).

Like a QR code? I hear it's all the rage in Japan (and catching on pretty fast here, too).

I made some cards for my photography: front is a little section of photo with a QR code to that particular photo on my site, back is my name and URL. But, as it happens, I haven't actually really used them yet –as much because paper is inconvenient as because photography is a hobby, not a business, for me.

I always end up throwing away business cards –small paper objects do not have any permenant place in any of my filing systems –but a physical object with easy and non-error-prone analog-to-digital conversion seems useful (especially if they have space for annotation somewhere on them).

I don't remember setting it, but it's set to 'never' already. I'll keep an eye on whether it really disconnects as often as I thought.
For reference as to how to set it: a quick google says: Settings>Wireless and Network>WIFI Settings>Menu Button>Advanced>Sleep Policy to Never .

Reading comments, the smartphone + data plan + commercial SIP sounds the most promising. Sometimes I like to Figure It All Out, but right now asterisk and all sound like a bit too much trouble. I did buy the Nexus S, and am (as expected) finding mobile internet/maps/e-mail tremedously useful (or at least fun). And, I barely talk at all –I've had a PAYG for the last two or three years –so having that on the side (and forwarding missed calls to it) might be a good backup for occasional loss of coverage.

The people in the Clear store said they didn't throttle per-service (I specifically asked about SIP/VoIP, and they also mentioned torrents), though I don't know if they're authoratative (or entirely knowledgeable; they misheard 'SIP phone' as ZipPhone at first). But yes, a detail that's important to check.

On the Nexus S, you can set Airplane Mode but (possibly with the help of an app) still turn WiFi on, which leaves me with a "no service" message on the unlocking screen, but avoids any later complaints. Perhaps that's something similar to be done on the E71?

That sounds like it might be a great option. I'm totally new to SIP. Any recommendations for SIP providers, or what to look for? (Of course, I can go do my homework, but...)

Cost per month with iPhone (AT&T):
$40 for 450 minutes
$25 + $10/GB over for 2GB
$10 + 10/ea for 1000 text messages
Plus residential internet:
~$40

Cost per month with Ideal Plan:
$40 for unlimited data

Good to hear it has potential to work. My concern so far is mostly the missing incoming calls: I often turn on the phone (just testing in the house) and see that the WiFi has disconnected, despite apparent strong signal. (However, Line2's pricing seems more straightforward than Skype's, though Skype is what I initially looked at.)

Another reason to move to Canada, then.

Informative indeed! I glanced at Virgin Mobile but glossed over them mostly; but that plan sounds appealing. I do already have the Nexus S, but it's still within the 30-day return window (and although I enjoy it I probably wouldn't be heartbroken to switch); however, it looks like it might talk to their network.

Any comments on Virgin Mobile's speed / restrictions on tethering?

Actually, I'm trying to have both, and have them be the same thing. When I'm at home, the Spot (or other mobile ISP) would be my home internet connection; when I'm mobile, it would be mobile broadband, as well as voice (over WiFi to my phone). So it's very informative (if sad) to hear that VoIP over mobile is jittery – which matches some, but not all, of the few tests I've done.