My experience with the Freerunner

[David Pottage]

On Tue, May 27, 2008 5:27 am, ian douglas wrote:
> ian douglas wrote:
>
> Since the call ended about the same amount of time as my test last night
> (236 minutes vs 234 minutes), I'm curious if either AT&T or TMobile
> simply kill a phone call just shy of 4 hours of talk time to free up
> their network.

That sounds likely.

With GSM the cost of a call is only calculated once the call completes, if
there is no limit on the length of call, someone who steals a GSM phone,
can keep a call going for several days, and the network only finds out
when they hang up. If the call is to an expensive international
destination ($2 per minute) The cost to the network could be high. Because
of this most networks limit the length of calls.

The details of the scam are described in chapter 17 of "Security
Engineering" by Ross Anderson. You can download a PDF copy from this page:

http://www.cl.cam.ac.uk/~rja14/book.html

Back to your test, As far as I know there is no limit on the length of
calls from landlines, so one solution would be to call the Freerunner from
an landline.

The other option would be to do what phone manufacturers do, which is to
measure the current drain from the battery, and calculate the talk time
from the battery capacity. Don't forget to be unreasonably optimistic
about signal strength, and battery life. :-)

-- 
David Pottage

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