Recent 763 flight in 2C - PAX in 1D (out of view of FA because of bulkhead) continued to text through the whole taxi - as we neared take-off roll I said "Would you mind turning that off please" to which the response was "Is this bothering you?" with my response being "As a matter of fact yes". Device was then stowed. This is not uncommon and if it is indeed an issue I believe the FAs need to be more stringent (but then the "self important" pax will likely complain. I find it common for phone calls and texting to continue well after the switch off announcement.