That's a second restriction -- I was referring to the first restriction.  From
the ATTWS website at <http://www.attwireless.com/umts/coverage.html>:

  Not included [in the Unlimited mMode plan]:

  * Connection to another device or computer via cable, Bluetooth, or
    infrared will be charged $0.001/KB.

  * You also will be charged $0.001 per KB if you remove the SIM card from
    your phone and use it to get wireless data service from another device or
    computer.

I think that second term is intended to apply to a device like a computer
that's capable of transferring lots of data (e.g., PDA), rather than simply a
different UMTS handset, but I don't really know.  (I haven't used the
service.)

BTW, the ESN of GSM mobile units is called IEMI (International Mobile
Equipment Identity).

Best regards,
John Navas

Well, that's not right either -- I was confusing the consumer "mMode"
(consumer data) "unlimited" plan with business "Mobile Internet" (business
data) "unlimited" plans.  (ATTWS reps concede that the plans and the website
are confusing.)

<http://www.attwireless.com/global/content/popup_mmode_terms.jhtml>
Consumer "mMode" "unlimited" ($25/month) is *not* limited to ATTWS-provided
devices and does include UMTS, but costs extra with a "connected" device
(e.g., laptop), although it's hard to see how ATTWS could actually police that
(other than by monitoring usage), as I noted earlier.

<http://www.attwireless.com/global/business/plans/popup_mobileinternet_terms_b2b.jhtml
Business "Mobile Internet" "unlimited" *is* limited to ATTWS-provided handsets
and ATTWS-certified PDAs, and UMTS is only available at the $80/month level.
The $25/month Unlimited Handset Plan, same price as the consumer plan, again
costs extra with a "connected" device (e.g., laptop).  ATTWS could obviously
police the use of "connected" since it provides the handsets.

There also a ton of restrictions on use in all these ATTWS plans that seem to
boil down to, "We reserve the right to terminate your service if you make too
much use of it ('unlimited' notwithstanding)."  Thus the simple T-Mobile
Unlimited plans <http://www.t-mobile.com/plans/default.asp?tab=internet>
($20/month added to a voice plan, $30/month standalone) look much more
attractive.  There's also unlimited T-Mobile HotSpot for $20/month on a voice
plan.

While checking this all out I had an interesting debate with a "data
specialist" who first told me that ATTWS would *only* sell service for
ATTWS-provided devices as a matter "policy" and (after conferring with a
"Supervisor") that she would therefore refuse to enter an order since I'm
using my own non-ATTWS Sony Ericsson Z600 handset, but backed down (after
conferring again with a "supervisor") and offered to try it when I pointed out
that ATTWS knowingly sold me service for that very handset, that no such
policy is documented in my Service Agreement, and that such an undocumented
restriction might constitute an unethical business practice.

Although I've generally had good to very good experience with ATTWS customer
service, this was a big exception -- it took me at least a dozen tries to get
past dropped and misrouted calls to someone that would take ownership, and
even then it took another 20 minutes to get good answers.  She confessed that
things were a "bit chaotic given the merger" and apologized several times.  So
persistence paid off, and all's well that end's well.