It would be convenient too indeed. However, I think the less the user has to touch the screen, the better tue ergonomics. With this method, each special character would require moving the thumb from keyboard to screen.

It would be nice if it could be combined with a way to cycle between special character shown in the popup vkb and select the one you want without moving your finger from the hwkb. In other words, pressing a then SYM would display âæäáã on screen, where you can tap to select if you're OK with tapping the screen, but â would be preselected, and hitting some key again (probably SYM) would select æ; and so on. When a character is selected in that popup, press any other key and it will be confirmed and show up in the text box at the same time that the other key. For instance, a, SYM, SYM, SYM, k and ! would result in äk!

One concern with your solution of hitting SYM after the letter though: how would you show all special characters on screen? With space then SYM? It would work.

Another way would be use SYM before the letter, and show all special characters (except accented letters, there are too many) whenever SYM is pressed, and then filter/show only the special characters (accents) corresponding to the first letter pressed after. One problem: to cycle special letters, you would have to move your thumb to SYM again which is awkward. Cycling with the same letter key again would create issues with a lot of words (I can elaborate if necessary).

Or if too difficult on the software side, then just hold SYM and hit a letter key to show corresponding special characters. Cycle by holding SYM and hitting the letter key several times. Show the full list of special characters (except accents) if SYM is hit then released without any combination with another key. This is my prefered solution, I think it's the most natural. [Edit] Well I realize it's exactly what has just been described for the N950. Could be combined with a vkb popup to tap on screen for those who prefer.