It might be easy to grow.  You can see many of this cute flower around Bangkok.   One of favorite of Bangkok Metropolitan Authority, I think.

Connie in Florida wrote;
Looks like Vinca to me. There is a rosy lavender one that grows wild here in Florida. I am always having to weed them from my garden. Sometimes, if lucky, a white one or a white one with a red *eye*will seed....these I keep. I had Phlox, when I lived up north and you definitely don't want them going to seed, because they are like petunias in that the seedlings are not true to the parent plant, but revert to a washed-out lavender shade. The *hot colors* of Vinca are popular here in Florida....such as the one shown in your picture....and usually supplant the impatiens, that wilt in the summer heat. These are perennial in our subtropical climate, becoming shrub-like and *leggy*, if not cut back. They don't seem to be fussy about soil and tolerate salt air quite well.
Connie

Mr. Shana Kongmun living at Koh Pangan wrote;

The Vinca is not a Vinca, it is a Catharanthus roseus or Madagascar Periwinkle.   Strictly tropical, while Vinca prefers cool temperate climates.

20 August 2000