1. If this was a fake by Apple, Google would have said something publicly to save face.
Maybe they're enjoying the fun? As long as Google themselves haven't made any official announcements, there's not so much face that needs saving.
2. It went through the FCC. Of course a fake FCC document could be made, but you cant fake the FCC web site that good.
I looked at the linked FCC filing. I've done FCC filings myself, this looks like it could well be a filing for an HTC phone with GSM, HSPA, Bluetooth (class 3) and Wifi. But is that itself meaningful... HTC is making so many new phones, they probably have a new FCC filing every month.
That filing actually asks more questions than it answers, too. I mean, this is NOT a world phone being described. Most of Europe and half of T-Mobile's G3 network is on 2100MHz, which is not supported by this phone. They do have G3 at 1900MHz (AT&T) and the other half of T-Mobile, at 1700MHz. Also in the 850MHz band, which is US as well, though not usually used for G3, due to the relatively crowded spectrum there. There's nothing but voice/G2/EDGE for Europe, and only halfway supporting T-Mobile. This sure looks like something made primarily for AT&T.
3. I have heard of some people running 2.1 on other devices already, so that at least is real.
I would not be the least bit surprised to discover that Google handed out Android 2.1 phones to employees. A fairly cool one, with AT&T support, and you have the potential of getting all iPhone-owning employees playing around with Android in one fell swoop.
4. There are pictures and video of the device running, but I guess they could be faked.
If you take away the back story, this whole "Nexus One" tale, the story that Google was all that involved in an HTC phone design, the idea they're going to sell this as a loss for some reason, direct to end users (but not properly designed to support T-Mobile? Yup, if you believe the FCC filing), then there's really nothing even remotely remarkable about this phone... just another good HTC Android phone.
Really, given the rumors about a "G-Phone" going back at least a year, it would not be very difficult for someone to put together a few actual facts and build a G-Phone story around them.
5. I beleave, I beleave, I beleave !!!!!!!!!!!!!!!!!!!!!!!!
I believe we are seeing pictures of Yet Another HTC phone, which is certainly an upgrade from some of the existing HTC phones. They do need that... they haven't put out a Cortex A8 phone so far, have they... I guess "Qilin", which is going to China, based on the same OMAP 3430 used in the DROID and the Palm Pre. But none here yet. So a Snapdragon or other A8 phone is a must for them, not a surprise, eh?
As for Google... a couple of things. The phone biz here is a bit wonky. For one, everyone evaluate the unlocked phone at MSRP, and sure, if you buy one, you pay MSRP. But that's because nearly every phone sold is subsidized. Real smart phones similar to the iPhone or DROID would run just a bit more than an equivalent iPod Touch, perhaps a bit less if you're not Apple doing the sale (other Apple gear typically runs at least twice the street price of comparable PC hardware)... maybe look at the Zune HD. Add a cellular modem, probably around $5.00, a $2.50 GPS chip, and ... well, you're pretty much done, give or take. Triple the cost to figure the impact on MSRP. It's not going to run $600, not even close.
With that said, does Google really benefit if they sell a phone at or below cost? I'm not certain they do, unless there's some other advantage there. They obviously benefit from ads and other Googlisms on Android, but Android itself is a boon to Google in fairly obvious ways: its rise is keeping someone else from dominating the cell phone OS, thus, the apps that run on the cell phone. Google's pretty savvy about the idea of search moving from the desktop to the phone, and they're totally dependent on search. Let Apple or Microsoft dominate the phone, and they could lose, not today, but give it ten years. Google's doing more to enable the value of a cellphone as a search device than anyone so far, between the voice-driven search on my Android home screen, Google Goggles, the barcode scanning stuff, other augmented reality, etc.
If I were to postulate on the "giveaway"... claim it's true, then explain it, I might guess... it COULD be a shot across the bow of the not-so-Good Ship Apple. In that, given a cheap, AT&T-tuned, unlocked GSM phone that just happens to outperform the iPhone, they might get a bunch of iPhonies to jump ship before their contract points them toward another iPhone upgrade. Personally, I find the Mot DROID and Verizon far more compelling, at the moment, but I wasn't struggling with AT&T or iPhones anyway, just waiting for a good Android offering on Verizon.