[clue-tech] bluetooth phone

[Nate Duehr]

On May 28, 2008, at 8:15 PM, David L. Anselmi wrote:

> David L. Willson wrote:
>> So, my phone and my Ubuntu Linux computer both claim to be blue in  
>> the tooth.  Can I
>> make them do tricks?
>
> I had a bluetooth phone and got it to do file transfers (I was  
> pretty happy to get the pictures off it before I gave it back).
>
> I tried to wing networking with a friend's phone but there wasn't  
> time to really understand what we were trying to do so it didn't work.


I've had my Bluetooth phones acting as modems for OSX and Linux  
(depending on the OS of the week) for a while now.  There were good  
references on the net, especially at howardforums.com for "tethering".

Be forewarned, if you don't have a "data plan" on many carriers,  
you're going to rack up a big bill REAL fast.  Also most carriers are  
not real happy about "tethering" and the CDMA carriers usually  
"cripple" the bluetooth in the phone to remove necessary  
personalities.  GSM, they can't do it as easily, so they monitor use  
and can cut you off (cut off your ENTIRE account) if they decide  
you're using more bandwidth than your data plan will allow.

Read the TOS of your carrier carefully and then decide if it's worth  
it to you to give something a try.

Meanwhile, back at the ranch... I have more experience with GSM phones  
than CDMA and GSM when both devices "see" each other with the right  
Bluetooth profiles, act just like modems.  There's a special set of  
"AT" commands (80's modem users will know what I'm talking about here)  
that the computer sends to the phone to establish the "modem" call,  
and then PPP takes over to give the link an IP address, etc.

By the way, the person who was saying their T-Mo phone was kicking  
them off after 5 minutes... play with the "keepalive" feature in your  
PPP scripts.  I forget which way it needs to be, on or off, and  
something in the back of my head says "off" not "on" which seems  
counter-intuitive, but one way will continually disconnect (because  
the GSM phone and back-end network, if I remember correctly don't  
"understand" what the keepalive is) and the other way will stay  
connected as long as you like...

I've not played with file transfers (different bluetooth personality)  
to/from my phones, I mostly just wanted a way to get online mobile...  
but that can supposedly be done too... within the filesystem limits of  
the phone, or an add-on memory card.

The other way to go these days, and "carrier approved" is to buy a  
high-speed cellular data card or USB "dongle" that has Linux kernel  
support and just plug it in... along with paying for their high-speed  
data service.  They like that a whole lot more.

I'm cheap... I had a old "grandfathered" T-Mo $19.95 "unlimited" data  
plan on their old low-speed network, and GSM can't really tell the  
difference as to which data network you're on, so as I upgraded phones  
and got higher speeds, I never had to answer to them for my data  
usage, which was still insanely low... pretty much only used when I  
couldn't find open WiFi or other means of high-speed access, or I was  
in the middle of nowhere and needed a quick SSH to something to fix  
it.  Later I switched carriers and had a low-volume data plan attached  
to that GSM phone and I use tethering sparingly to that phone.

In general, the carriers are getting "grumpy" about high-use data  
customers "tethering" to phones that have lower use types of data  
plans associated with them.

The "best" behaved carrier for years was Sprint who for years and  
years said "unlimited" as long as you had one of their data plans, and  
typically they didn't cripple their CDMA-based phones... but they  
announced last week that they're putting a 5 GB/month "cap" on that  
generosity, even for "unlimited" usage... there's just not enough  
bandwidth to go around and the carriers need that bandwidth for the  
business and other customers willing to pay an additional $50-$70 a  
month to have a wireless data "dongle".

If you're going to play with it, go for it... but tread lightly.   
Search Google for horror stories of people getting "customer service"  
letters telling them that some magician in the back room of the  
carrier deemed their usage "too high" and cut off their entire  
account, never to return... then you pay penalties for "early  
termination" and have to deal with waiting for your number to be  
ported to a new carrier, buy a new phone, etc... not pretty.

With all that said, though -- if you can use it responsibly and  
lightly, tethering to the phone is a nice trick to have in your back  
pocket when you're really stuck and need a way to check something.  Do  
a lot of research and figure out which phones can tether by hunting  
around the net...

--
Nate Duehr
nate at natetech.com