Love questions like this because I'm such a nostalgia hound. My first cellular phone was a Samsung SCH-3500 on Sprint. I got it when I was 18, about a year after it debuted, and I chose Sprint because at the time they were the only carrier not doing credit checks (plus, at $129.99, the phone was pretty affordable). Despite its poor reception and volume (and Sprint's nascent network), I loved that cool-looking thing. I'd post a picture but the in-flight WiFi I'm using is terrible and it would never get through.
My first smartphone came three years later. I'd moved to Virginia for college and snagged a job with Nextel. Nextel would later be acquired by Sprint, but at the time it was very healthy, growing explosively ... and it offered a free phone with free service to every retail employee. To augment that i60c "Employee Business Phone," I picked up a BlackBerry 7520 on one of my $10/mo friends & family plans. It was a huge clunker with terrible battery life and 19kb/sec data speeds ... but it was my first smartphone and I loved it. I still remember people being surprised to learn I could check and respond to email instantly from my hip – and use PTT on the same device!
As for phones I've bought with my own money ... man, so many. From 2003-2012, I was buying a new phone at least once a year, and some years I hit 4 or 5. Eventually it just made more sense to get a job where I could use a lot of phones without paying for them.
I feel like it was one of the first mobile phone companies I was really aware of. The V60 was hot business when cellphones were becoming a "thing," and it was backed up by a pretty aggressive ad campaign ("HELLOMOTO!"). Plus, Nextel was big in my market growing up, and it was kind of hard to ignore those "walkie talkie phones," all of which were made by Motorola at the time.
Once I started working for Nextel it snowballed from there – and the RAZR/SLVR/PEBL/Q era kept me interested thereafter. Every time I'd sort of fall off on Motorola, they'd do something else interesting: Moto Droid in '09, Droid X in '10 ... even the Photon Q for Sprint was pretty cool. But it was with the release of the first Moto X that the company really earned my love. That phone, and the Moto X 14, were the best damn phones I'd ever used. I still power up my '14 on occasion and I'd still use it today if the camera were better. What a beauty.
I started off with a Sony Zuma with Verizon (Airtouch? GTE? Pre-Verizon days).
Motorola V200 - looked like a pager, full QWERTY. Needed to use a headset or all calls would be speakerphone. This was like three years before "quick messaging" phones were a thing.
Motorola T720c - the CDMA variant. I wish it was able to use the camera attachment that was available for the GSM models worked. Still - Moto Mods? You could swap the plates with and flash firmware for the T730 to update it.
Motorola V710 - controversial because it had Bluetooth but not the profiles to transfer files. Did have a "TransFlash" slot though.
Motorola E815 - essentially the EVDO update to the V710. I remember tethering my (monstrous) Toshiba Qosmio laptop during my college days for fast internet. lol.
Motorola RAZR V3c - being a Verizon customer, the RAZR craze came a bit late but yeah it still felt cool to own.