I bought this unlocked phone in UK(actually one from Carphonewarehouse, they sell unlocked phone at the same price as any network version. And the other from Amazon.co.uk), hoping that I could use it when I return to USA.The phone is light, and COMPACT. I can walk without any silly bulge in the pants. It works in Android 4.0, with a clear call quality, and its the Beat sound, left on the tabletop, is loud enough. In UK, it works on 3G network; whatever the signals UK networks(3 network, virgin, vodafone UK) send, it worked  fast to guide me to anywhere with travel/navigation apps. And, I was told this would work with T-mobile and AT&T in USA. I was re-confirmed by a verizon store staff that this will NOT work with Verizon as their network phone comes with no sim card.It is not a shabby phone at all. I give 4.5 star for their compact yet full features I have enjoyed in UK.___________________Upon returning to USA, I searched for the network that would work with this phone.As a decade of AT&T (former Cingular) customer, i could pick $20 data plane that simply adds 300mb/month for a quick tryout(call plans, separate, and unfortunately, no sim card only bargain plan was availe like T-mobile) but this one gets registered in 2-3 min phone call, but the data is only awkwardly slow. AT&T technicians tried to help further but, they repeatedly say "since this is NOT one of our network phones, we cannot provide further..."The only signal I get is E(Edge=2G speed) signal. How disappointing!The representative said ''GSM acceptible'' in the HTC production info means Edge(2G) connection. And their 3G signal in USA won''t be the same one as UK networks carry. Even though it says 3G, it is not quite compatible. That is a big bummer.Anyway, to get connected to AT&T, you will need regular-size(UK size) blank sim card from AT&T store. If you ordered a sim card, there will be $3-7 extra charge.As I was long out-of-contract AT&T customer, there was no Activation Charge($35). Once you accept the smartphone sim card, you can still drop the data plan and go back to non-smart deal(I doubt I will) and it will require another sim card, the company says.The next best option is go phone with $50 Unlimited everything plan but they will have to honor Desire C, which I didn''t try yet.____________Alternatively, to get connected to T-mobile, there is a sim card only plan, starting from $70/$90/$110. And, they require 2 year contract. Not for me yet.You can also try their pay as go plan at the competitive rate. But, my search just ended there to try out this AT&T 300mB at additional $20. And, I can change it to 3GB at $30 whenever or vice versa.I set the connection priority to Wi-Fi vs. AT&T network so that it doesn''t consume the data plan I joined much. And, that is cheaper way to use Smartphone on AT&T instead of $40 smartphone charges and further $45+ monthly fees  they are introducing with Shared Data Plans. Greedy, I must say._______________________Final thoughts.I am still satisfied with Desire C''s speed on my wifi (thanks to Comcast plus internet service at home). And my 2G connection in anywhere else is barely acceptable with spotty downloading speed(Google Navi locator took 30sec-1min to pinpoint where I was. TED(streaming) would never play on my screen with 2G).So, even though I like the handset, this 2G connection speed in USA should be your key consideration before considering this phone.If you are outside home all the time, never near wifi, this is not going to be your best buddy, unless you find a good use of it in other countries like I do.