My Sony Ericsson C905A (AT&T variant). It was a pretty unique phone, being one of the first to have an 8mp camera, and also sported a xenon flash, so you could take proper photos at night. I took some pretty nifty pictures with that "phone" back then, when most people were still using 1.3mp or 2.0mp camera phones.
It had its definite flaws. It required a proprietary connector to charge/sync, and used that connector with an adapter to use headphones or aux audio jack (which it didn't #$^%ing come with). It also used Sony's Micro M2 instead of microSD, which cost quite a bit more.
In addition to loving that camera/phone, it was a gateway device for me. Back then, for me a phone was just a phone. Texting too, of course. I rolled my eyes at iPhone and BlackBerry users that needed to stay connected all the time. But part of the deal when buying that phone was it was only $50 on-contract ($350 off) if I signed up for the internet option (which didn't use "data"), which was $15/mo, for 6 months. So basically, paying $140 for the phone, then I'd cancel the internet. But soon I realized that having internet/email in my pocket was extremely handy, even on that dinky, low-res screen, so I kept for the life of the phone.
Unfortunately, the life of the phone was barely over a year, after somehow the LCD cracked and started bleeding (no idea how, I never dropped the phone). When I called for a warranty replacement, they no longer offered that phone, and tried to pawn off some Samsung slider with a paltry 2.0mp camera. I explained that the reason I bought that phone, and in fact switched from Verizon to AT&T was to get that phone. So I was offered a Sony Ericsson Xperia X10, which had literally came out the day before - simply because it also had an 8mp camera. I thought there was no way I would be offered that phone, but when they did, I said "uh...yeah. Sure."
That Xperia X10 was great at first, but slowly died (despite being given a brand new one, not a refurb), and its replacement died a quicker death. But it was my first smartphone, and I've never regretted getting into Android.