What's interesting is that in Europe, DECT was designed to work the same way, but it never caught on as anything aside from a home cordless phone standard. Wikipedia says there was even a public DECT network in Italy until 2001.
Checking the Wikipedia article for walkie-talkie just now, it seems the formal name for it is "handheld transceiver", so it makes sense that "handy" would derive from that.
Edit: I was too lazy, scrolling down a bit on the same article mentions and explains the term "hand[y|ie]".
I think most native speakers who aren't technical would pick something from that list which probably doesn't have "USB" in it and then wrap it with "little" and "thing" - eg. "little thumb drive thing".
When talking to some of the US customers they use it as well. It is not as popular as USB stick or Flash drive, but still quite common.
Everyone I know says flash drive or USB stick or thumb drive, roughly in that order of popularity.
Maybe you are talking about tech people. I am talking about mix.
Well, they both refer to hands, I guess. The Chinese word is 手机 shouji "hand machine". "Phone" is 电话 dianhua "electric speech". Those two words aren't related.