The problem with paid WiFi hotspots is that the one-off cost and hassle of getting access can often be too high. In theory, the session-based approach is quite elegant as it affords the user plenty of choice, but practical and economic constraints mean it's often poorly provisioned in reality. And it's almost impossible to sell ongoing WiFi subscriptions to massmarket users - you can never be sure of the availability of (say) BT Openzone or T-Mobile or Boingo, and roaming isn't perfect.
Conversely, the problem with mobile broadband (HSPA) is that generally it is only available on a subscription basis (or sign-up-to-a-specific-operator prepaid in a few countries). In addition, data roaming charges are often prohibitive, you can only access a given carrier's network even if others are available, and you may have to deal with lousy operator-specific connection manager software.
When you just want to access the Internet from a laptop, there is almost no reason to haul all the traffic through an operator's core network - especially backhauling it internationally to your home operator's GGSN. It should just be linked out to the Internet at the closest and cheapest connection point to your present location. Sure, some services may need to be routed back (eg operator-specific messaging or VoIP), but the bulk of traffic should be able to transit the most convenient access. [And yes, I know there's always lots of industry blather about content filtering, but I see no reason why it should apply to laptop 3G but not laptop WiFi].
There is an urgent need for HSPA/EVDO session-based broadband access. If I travel to the US, I want to be offered a menu accessible from my PC, with with T-Mobile and AT&T competing to provide me mobile broadband access for the duration of my stay - and maybe Verizon & Sprint too if I've got a dual-mode modem. I don't want to be confined to whichever happens to have a roaming relationship with my UK operator. Sure, I want that as an option, but there's absolutely no reason to be locked in to it. I want lots of different payment models - the hotel cuts a deal with AT&T, maybe my client has a guest HSPA network with T-Mobile via a picocell and so on.
Initially, I thought this operator-neutral approach to mobile broadband could be achieved with local, cheaply-bought extra 3G dongles. Buy one (or rent one) at the airport on arrival, preloaded with SIM and 5GB / 5 days / whatever, and drop it in a recycling bin on the way out. Maybe even get one lent to you for an hour with a cappucino, or given free to you as a conference delegate (as per the GSMA's approach to some analysts & journalists in Barcelona). But my recent experience with clashing modem drivers and dodgy connection managers has made me rethink this.
In a nutshell, 3G modems, either built-in to laptops or as separate modems, need to be able to easily and switchably support multiple operators. No software glitches, no need to get an extra SIM card from a shop or by mail, no onerous registration tasks. Sure, some people will opt for the subscription route anyway because it meets their needs precisely, but there need to be alternative models as well.
I think the WiMAX guys already "get" this. But a lot of mobile operators are still beholden to their custom modems and software clients and SIM cards. They need to face up to the reality that mobile PC users are different from mobile phone users - there's no need for a consistent inbound phone number, and therefore much less need for a continuous relationship with just a single service provider.