Google's Open Source Mobile Platform
As expected, today Google took the wraps off of the gPhone (as the media have for months been referring to the rumored project). Google is "leading a broad industry alliance to transform mobile phones into powerful mobile computers," and will be licensing its software to all comers on an open source basis under the Apache license. (The Wall Street Journal's Ben Worthen demonstrates a miserable grasp of what "open source" means.) Google's US partners include Nextel and Sprint, but not AT&T nor Verizon. Phones will be available in the second half of 2008 — not the spring as earlier reports had speculated. News.com's analysis warns that Google won't take over the mobile market overnight, though they quote Forrester in the opinion that Google may be one of the three biggest mobile players after several years of shakeout.
An old-timer with old-timey ideas.
I don't have any experience with Sprint but T-Mobile is probably the best in terms of being "open" of the big four mobile operators in the US. For example, until a few years ago you could get free web browsing through them by exploiting a hole in their free WAP access service. Instead of just shutting the hole and ignoring the people who didn't want to pay for a full Internet plan, they decided to shut it while transitioning to tiered Internet plans so people who didn't need to tether could still get the full web on their phones at a reduced price. Most phones also apparently will still let you tether with their cheap service, though T-Mobile will cut off your access if you use too much bandwidth while doing this.
They use GSM which is a big plus if you want to buy your own phone. I haven't yet needed to because, while all of their phones that I've owned were locked and had T-Mobile logos and "premium services" everywhere, none of them were in any way crippled like Verizon is infamous for doing. I even added a custom ringtone to one of my phones using only a standard USB cable and the manufacturer's ringtone transfer software. Their coverage is pretty good, the only time I've had trouble with it was when I was traveling through West Virginia which is a hard area to cover with cell phone service anyways. Their biggest problem is that they don't yet have any 3G service available anywhere (they're waiting for the spectrum they bought for it to become available for their use) and their customer service is nothing to write home about, but that's pretty much par for the course in this industry.
What if this signature were clever?