With the new iPhone OS 3.0 now available for download, AT&T support for MMS and data-tethering remains conspicuously absent. While some might attribute this to greed or laziness on AT&T’s part, the reality is that AT&T’s network still isn’t capable of supporting millions of iPhone users sending large volumes of video and photo MMS messages. Add in data-tethering, and AT&T likely has a very real fear that its network might collapse under the weight of Internet savvy iPhone users.

Compared to other smartphone owners, iPhone users not only go on the Internet more often, but tend to browse for longer periods of time and download more mobile content in the process. According to Roger Entner, a telecom research analyst for Nielsen, AT&T’s network still isn’t prepared for an onslaught in data consumption. In an interview with the USA Today, Entner points out that the average iPhone user consumes upwards of 400 MB of data every month. In comparison, most smartphone users only consume around 40-80 MB of data every month.

It’s important to remember that the iPhone isn’t the only smartphone AT&T supports. That being the case, it’s very likely that AT&T views the iPhone as already eating up more than its fair share of resources, and is reluctant to add support for new features that would only increase that data consumption.

At the same time, iPhone users pay a pretty penny to AT&T every month, with the average bill coming in at somewhere around $90 a month. Moreover, the iPhone attracted a large number of new AT&T customers, and though AT&T subsidizes every iPhone sold, it’s able to make up that difference in only a matter of months. You would think that with all of that moolah, AT&T would have been busy upgrading its network infrastructure to prepare for new iPhone models that it undoubtedly knew were in the pipeline.

AT&T has more iPhone customers than any other carrier, so it’s not necessarily fair to compare it to all the other carriers that will provide immediate support for MMS and data-tethering. Some have even suggested that perhaps AT&T isn’t moving too slow, but that the iPhone is growing at a faster rate than AT&T could have ever anticipated. While that might sound nice, the iPhone has been out for almost 2 years now, so the excuse that “AT&T isn’t ready” is kind of played out at this point.

As a final point, data tethering is already supported by AT&T on a host of other phones, but the iPhone remains the odd man out. What’s confusing about AT&T’s silence on the matter is that iPhone customers are more than willing to pay a few extra bucks a month for the feature.

Perhaps after the debacle that was the iPhone 3G launch last summer, AT&T is indeed keen on implementing MMS and tethering, but wants to make sure its network is more than capable of handling an insane amount of data before it makes any promises it can’t keep, and subjects itself to even more lawsuits. Still, it was less than a month ago that AT&T released a press release touting all of the upgrades it was making to its network. If by summer’s end, AT&T support for MMS and tethering work flawlessly, we might look back and see that we were too hard on AT&T. But if MMS and tethering support are riddled with bandwidth problems, well then Apple will be counting down the days until its exclusive contract with AT&T expires.