Few companies/organizations have made much of an effort to cater to the mobile use case, let alone specifically support it.

Dev teams may have dabbled with it, but the reality is the demand from users (traffic wise) wasn't there, and from an ROI perspective the return didn't justify spending much QA time testing it, let alone developing views optimized for low resolutions.

The traffic (as a percentage of overall traffic) still isn't there, but we're starting to see end users beginning to experiment more with what they can do with their mobile devices. Obviously iPhone opened up playing field, and as the next gen Palm, BlackBerry, HTC, and Android devices grab market share we're seeing users give them a try with our online web applications.

Assuming mobile traffic becomes substantial enough to warrant catering to this use case, how does that affect the SDLC?

From a development perspective, this is where your efforts in MVC are going to pay off as you focus on building different mobile views.

As for the testing portion of development, and QA itself, obviously these are tremendously impacted. I'd expect to see test automation tools that can simulate different devices, OS's, and browsers. Similarly emulation tools that show you what it would look like on such a device; without it you'd need to buy all the devices you support, and they're coming in over public internet which typically your Dev and QA environments aren't exposed to.

It's still a ways to go before these become a serious challenge that Dev teams need to deal with, but as it ramps up over the next few years and it'll be interesting to see how teams and tools adapt.