For maximum mobility and convenience, the #1 choice of the road warrior is EVDO or HSDPA. These wireless standards are the direct replacement for the "1xRTT" cellphone data service, which topped out at about 100kbps download speed (not at all shabby by modem standards, but it's not really broadband, is it). Current EVDO Rev0 systems (most of the US) max out at about 700kbps down and 150kbps uploads, but just around the corner is EVDO RevA, which boosts the upload performance dramatically; HSDPA performance is comparable. Future revisions to both standards are supposed to rival wired connections for speed. Meanwhile, if you wander out of an EVDO coverage area (most metro environs, airports and highways), your card will automatically fallback to 1xRTT connectivity. Note also that EVDO is based on the CDMA cellphone standard, which is limited mostly to the US of A; HSDPA is an outgrowth of the international GSM standard, so in theory it will work internationally.
There are currently PC Card and ExpressCard EVDO & HSDPA solutions for mobile Mac users from Verizon and Sprint (EVDO) and Cingular (HSPDA), with equipment costs around $100 and monthly service charges around $60 a month for 'unlimited' service; the drivers are even built-in with OS X 10.4.9 and the WWAN update. Until recently, Cingular's support for HSDPA on the Mac was limited, but the AirCard 870 is supposed to work with the WWAN Apple drivers. If you've got a PowerBook G4 and you're thinking of upgrading to a MacBook Pro, you can get the ExpressCard form factor with a PCMCIA adapter and future-proof yourself. What if you've got a machine with no card slot (iBook or MacBook), or a desktop machine? Fear not: Verizon, Sprint and Cingular now all sell USB-connect versions of their cards, which work with pretty much anything.
If you want to share an EVDO connection amongst several of your computers, you can use the built-in Internet Sharing feature of Mac OS X, or for several dollars more, both Kyocera and Linksys sell WiFi routers that sport a PC Card slot for an EVDO card. You let the router handle the wireless WAN connection, much as old Airport base stations could dial up your ISP, and you just connect over the standard WiFi support -- so easy, and great for an RV or field production office. Check out EVDOinfo.com for current pricing and card availability.
A card or USB dongle isn't the only way to get EVDO/HSPDA into your Mac; some cellphone models support direct tethering for broadband on the Mac (not as many as Windows, sadly), and we noted a Blackjack tether solution late last year. You can see a list of the Verizon models that support tethering (also sometimes called DUN for Dial Up Networking) at this driver download page. If you've got a Palm-based Treo 680 or 700p, you can tether your Mac via Bluetooth or via USB with the PdaNet package, and there are plenty of third-party guides out there for other Treos; however, the 650 offers only 1xRTT speeds, or slower in some cases. Blackberry users have fewer tethering options; you can either use a Bluetooth tether and a separate proxy server, or (on Intel Macs) connect the Blackberry in Parallels and back-share the connection to the Mac. Weak!
Speed: Good, getting better with EV-DO Rev A and future HSDPA releases
Coverage: Almost universal for 1xRTT, major metro areas and airports for EV-DO (see EVDOinfo.com for latest coverage areas), more constrained for HSPDA
Cost: Moderate, $60/month in most cases
As a replacement for cable or DSL service to a specific spot, your best choice is fixed or semi-permanent wireless (WiMax or similar) like that offered by Towerstream, Clearwire or other vendors. If you're in the coverage area for one of these services, you can get premium bandwidth over-the-air. Clearwire will also let you move your antenna from place to place within the coverage zone; Towerstream, marketed and priced for business use, requires a permanent antenna install. From the Mac's perspective, these services -- provisioned via a standalone modem and Ethernet-out -- appear just as a cable modem would; both can also be connected to a local WiFi network without difficulty.
Speed: 1.5 Mbit down (Clearwire), up to multiple T1s (TowerStream)
Cost: very high (TowerStream), moderate (Clearwire)
The next best thing to a direct fixed-wireless connection is roaming WiFi or community internet, where you can piggyback on an existing deployment of base stations to get your broadband fix. The most well-known of these deployments is probably T-Mobile's HotSpot service, which lights up every Starbucks and FedEx/Kinko's location with those sweet, swift megabits; others include Boingo, iPass and Wayport. All offer daily or weekly pass pricing in addition to a standard subscription plan; T-Mobile charges range from $40/month for month-to-month unlimited access, down to $20/month as an add-on to your existing T-Mobile cellphone service. In either case, if you happen to live within 100 feet of a Starbucks (who doesn't?) or you're a member of the digital bedouin class, this might be the solution for you.
Another approach to shared broadband is community or share-alike WiFi, where municipalities or individuals choose to provide service that's available to all. I'm particularly interested in Fon, a share-alike service where you install one of the company's $40 custom routers and then gain free access wherever others have done the same. For community internet projects or other free access in your neighborhood, check out nodedb.com or jiwire.com and see maps & lists of access points. Please note that when you're using a shared access point, it's bad form to run bandwidth hogging applications such as BitTorrent clients.
Speed: Varies by location, generally good
Coverage: Point coverage
Cost: moderate, offers on-demand pricing with daily passes/free in some cases
For the extreme high ground of broadband, there's nowhere to go but up: Satellite broadband service from providers like WildBlue, HughesNet (formerly DirecPC) and StarBand can get you online in areas where no other connectivity options exist. These are fixed installs, not roaming: the satellite footprint covers most of the continental US, but the back-channel 'squirt' requires fine antenna calibration. Speed offerings vary, with most services starting at a baseline 512Kbps download rate and going up from there with premium pricing. The service isn't suitable for gaming or VoIP use (high latency caused by the trip from geosynchronous orbit) and the initial equipment installation can be pricey ($400 or more in some cases). Still, if your fishing cabin/fortress of solitude/bomb shelter is out of reach of the standard connectivity options, going orbital might be the best choice.
Speed: Comparable with EVDO or DSL (512Kbps + download)
Coverage: Nigh universal, assuming you have sky sightlines
Cost: Moderate ($50/month) but high startup costs
Good luck unplugging! If you have an interesting or terrifying Mac wireless networking setup, let us know.