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You don't *honestly* think that you're going to get WiMAX coverage everywhere you go, do you? WiMAX isn't magic. It has most of the same limitations that regular 802.11 b/g has. It's an *improvement*, but you still aren't going to get good signal inside of most public buildings.

Unless you barely use your cellphone, you'll find that the netbook's battery is
your biggest limiting factor. Particularly if you use a bluetooth headset so you aren't walking around
with a cabled headset plugged into the netbook. There are 802.11 based SIP phones that can serve the same purpose.

You say:

Are there any obvious problems you would foresee?

and then a sentence later:

A major issue is, of course, the fact that my pseudo-netbook has to be carried everywhere and left always on.

I would consider this a pretty big obvious problem.

Because they're not ubiquitous. You will end up somewhere where coverage isn't so great for your new protocol. If you can handoff to an older protocol, you will keep your connection. So this is why even a few years ago you could get Verizon phones that still supported AMPS, why every phone that supports EV-DO also supports 1X (and older standards), and why every phone with WCDMA/HSDPA/HSUPA/etc still supports plain old GSM/GPRS/EDGE.

It's also why it doesn't make a lot of sense to have a WiMAX only phone. You need at least WiMAX+GSM, or WiMAX+CDMA1X. You need to be able to hand off to the older interfaces. And probably you want to support everything... WiMAX when it's available, HSDPA or WCDMA when that's available but WiMAX isn't, or GSM/GPRS/EDGE when that's all that's available.

Or maybe you never leave downtown Atlanta. Then maybe WiMAX-only would be fine, assuming you trust the reliability of the relatively new network.

The CP Lawn Bowling Club in Victoria, BC has done this. WiMAX -> Buffalo AP -> Linksys PAP2T -> SIP provider. Bringing the monthly bill from $54/month with Telus on copper pair, to $35/month for unlimited long distance and broadband/wifi as well. http://cplawnbowling.org/ [cplawnbowling.org]

"Oh my god, someone call 9-1-1!"

"Hang on, let me get my computer out of suspend...

And put my headset on...

Ok, I am dialing...

Hello, yes, emergency-- What? You are the 9-1-1 dispatch center where? Tulsa?"

Portland, Oregon, also has WiMax through Clear. There are decently large sections of Portland (including my house,) that do not have WiMax coverage; and larger sections with very spotty coverage. Admittedly, Portland is a much "hillier" city than Atlanta, but it only stands to reason that some parts of Atlanta would have coverage that leaves much to be desired, as well.

The 911 problem others mention can be resolved by picking a VoIP provider that has 911 service; or by manually bookmarking your local phone number for emergency dispatch.

WiMAX was designed to handle VoIP traffic, and has specific traffic categories on the airlink for isochronous flows, like RTP and other VoIP payload streams. Unlike something like Ethernet, which is CSMA/CD (carrier sense multiple access, with collision detection), traffic is scheduled by the carrier network. For uplink data, your WiMAX card goes through a process of requesting bandwidth on what amounts to a hailing channel, and then gets a bandwidth allocation it can use. In theory, a small but constant amount of bandwidth can be allocated for VoIP at the airlink level, resulting in low jitter, low latency, and low frame loss.

There are a couple of problems with this.

The first problem is that not all WiMAX cards on the market today (in fact, quite possibly none of them) have sufficient sophistication in their device drivers and microcontrollers to send the RTP (or Skype, or whatever VoIP protocol you're using) packets on an isochronous service flow while the balance of the packets travel on a general-purpose service flow. As a result, the RTP (etc) packets have to compete with whatever else your machine is doing, either stuff you're initiating with the browser, or background things like checking email or updating the Vista weather widget, or checking for updates of one kind or another. It doesn't help matters that no operating system has a network stack that implements the service flow concept.

The second problem is that low-speed isochronous flows over the WiMAX OFDMA airlink depend upon sharing a fairly large timeslot with other users transmitting simultaneously on the uplink using a different set of carriers, at least if the system is going to be economically feasible for the carrier. Allocating an entire timeslot often enough to keep the delay below half a second or so would result in considerable wasted bandwidth, so the idea is to have users share a timeslot by have each one use only a fraction of the available carriers. Decoding the resulting burst at the base station then depends upon maintaining orthogonality between OFDM carriers, which means that exact frequency synchronization is required between multiple users. While each user's WiMAX card synchronizes its clock with the base station, doppler shift due to changes in speed or direction or a changing multipath environment can change the received frequency at the base station enough to compromise orthogonality and make the burst impossible to decode.

The result of all this is, from your perspective, is that your VoIP traffic could be jittery and have long delays and high packet loss, especially when the carrier's network is heavily loaded.

Have had this discussion with Clear already. You can roam anywhere on their networks - as long as you're in Atlanta or Portland Oregon, the two cities where they have a presence.

Was thinking about WiMax as a solution to mobile connectivity for my laptop, until I realized I'd have to set up different service in the different cities where I want to work (and would have to wait until some of those cities have WiMax in place). FAIL.

Not like I want to pay for 3G, either.

I figure in 10 years, a lot of this gets sorted out. I'll put the MacBook Pro on standby 'till then, k?