Which is what used to be called, more clunkily, "using your phone as a modem".
This isn't especially new - it's been possible since the days of GPRS at least. On the other hand, it's often been an enthusiasts-only sport, involving various configuration hassles (Bluetooth, non-standard cables and so forth), which while theoretically simple, have been enough to dissuade most potential users.
In the past, this practice has been viewed differently by different mobile operators. Some have actually encouraged it, because their “phone” data plans have been more expensive than their “PC modem” data plans. Others have limited the practice via terms and conditions, especially on uncapped “flatrate” data plans for devices like the Apple iPhone.
More recently, a variety of phones like the H3G Skypephone S2, and the Palm Treo Pro, have been designed specifically with tethering as a key usage case – they even enable the driver software to be loaded onto the PC automatically (rather than needing CD or separate download/install) and ease configuration through wizards and so forth. Some operators see them as a good way of enabling two devices via a single subscription – and help them upsell the user to higher bandwidth-cap tiers or faster speeds.
However, Disruptive Analysis believes that this approach (and other approaches to using ‘clusters’ of linked devices, for example in a “personal area network”) will remain in the minority. In particular, the use of a phone as a tether, attached to a PC on one side and a 3G connection on the other, is likely to exhibit a high degree of battery drain – although it possible that they could also draw energy from the notebook battery if a physical cable is used rather than WiFi or Bluetooth. However, where a cable is used, it makes it awkward to have a simultaneous phone call – and some implementations of 3G chipsets may not even permit two connections to run concurrently.
The price of modems/chipsets should come down to a point at which it’s just simpler to have multiple ones for multiple devices. Where it may become more important is in emerging markets, where a single 3G access could feed multiple users via WiFi.
Nevertheless, this approach gets around the issue of “lock-in” for embedded mobile broadband in notebooks – users tend to upgrade phones, and/or churn providers, once every 18 months or so, which makes it easier for the computing element to benefit from upgraded modems without disassembling the PC to the change the module. On the other hand, implementations of new wireless standards in phones often lag those in modems, especially in mainstream devices.
In a way, tethering could be a partial answer to the issue of session-based MBC without the need for a separate SIM card in a notebook or dongle.
Overall, the tethering approach using a handset is likely to appeal to some Mobile Broadband Computing (MBC) user segments and operators, but it seems unlikely to displace either external modems / dongles, or modules embedded in notebooks or MIDs. Disruptive Analysis is skeptical that tethering will be used by more than perhaps 10% of regular MBC users – although if useability becomes better, it may be used on an ad-hoc basis by a larger number of people with an occasional need for connecting a PC or other device.