[8525, TyTN, MDA Vario II, JasJam General] id242:
I found this about a month ago when I was looking for an answer to this similar question (but regarding tethering with a laptop & dataplans). I post it here in an effort to share something that may be useful to others with similar questions.

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What AT&T doesn't tell you is that all of the data plans are the same, they all work the same way, and there's no difference between the $20 media max data plan, $40 pda plan, or $60 laptop plan.

Well almost none, there is one difference which I'll explain. But the point is tethering or not, you'll never be charged a single penny more than your flat unlimited rate no matter what you do.

AT&T doesn't differentiate tethered data vs. phone-originated. To them it's all used the same way. The phone logs in to the data APN and uses data and in some case that can be coming/going to the laptop.

Officially for tethering or laptop data cards alike, you're supposed to have the $60 "laptop connect" aka "data connect" unlimited plan.

So what's the difference?

Here's a little primer on data plans.... AT&T has 3 access points (APN's or Access point names.)

1) wap.cingular

2) isp.cingular

3) blackberry.net

#3 is only on blackberry plans and it's necessary to use blackberry connect for your Treo if you were to try to use it. Otherwise, it's not interesting for this discussion.

For ALL AT&T phones (flip/bar phones,) Windows mobile, Symbian, Palm OS, laptop cards, and tethering.. in other words EVERYTHING that's not a Blackberry, they use APN #1 and #2 above (wap.cingular or isp.cingular.)

wap.cingular = NAT IP address. Basically IP address sharing you find on any corporate or home router.

isp.cingular = Public IP address. Exists for the purpose of supporting VPN clients, some of which have trouble working over NAT.

wap.cingular is intended for use with all phones, PDAs, etc.

isp.cingular is intended for data cards and tethering.

However, they're not mututally exclusive to those operations. You can use a phone on isp.cingular and tether on wap.cingular for example.

OK, now the data plans:

$20 Media Max 200 = wap.cingular only

$40 PDA "personal" Max (1500 text messages) = wap.cingular only

$40 PDA Connect Unlimited (aka PDA39) (no text messages) aka PDA enterprise = wap.cingular + isp.cingular

$60 laptop plan = wap.cingular + isp.cingular

Any plan with "tethering" will include isp.cingular + wap.cingular.

Any plan with "Personal" in the name will be wap.cingular only.

OK so what does all of this mean?

None of this means anything except that I'm trying to explain how the different data plans aren't different.

If you have a data plan that includes isp.cingular, you can use as well as tether on isp.cingular. If you have a plan with wap.cingular only, tether and only use wap.cingular, never use isp.cingular.

On plans that don't include isp.cingular, it should simply fail to connect. But to be safe make sure you don't see any kind of "internet pay per use" or similar wording on your features list. that would mean wap.cingular is unlimited and isp.cingular is "pay per use" rates.

This is how you'd get burned by a big bill and how people have been burned in the past. But AT&T seems to have fixed the problem and no longer put isp.cingular PPU on accounts anymore.

Just simply be aware of this so you can avoid it.

What APN you're using, you'll have to drill down in to the connection settings. The profile "My ISP" as well as "Media Net" are both set up by default to use wap.cingular (aka works on all plans.) Media net only differs in that it's set up to use a proxy.

You can also get more on this on a page I published here:

http://www.gadgetech.info/wireless/cingular/data/

Note, this is outdated. it was written before they introduced "PDA Personal" Max, so it doesn't reflect those new plans. But it is still educational if you want to know more about the difference between APNs.

Having said all of that, I have Media Max 200 and have had it for 4+ years on Treos. I've tethered, and use my SIM in laptop cards. I've never been charged extra. to be charged extra would be a billing error that AT&T should resolve.

PDANet is the easiest way to tether on a Treo 750.

When you get the WM6 upgrade, it has internet sharing built in which takes away the need for PDANet.

Note on WM6, the use "My ISP" not "ICS." "ICS" is set up to use isp.cingular.