I beg to differ. I used to think that the lack of a smartphone app was a deal-breaker. However if resources are tight I would firmly vote for NOT to developing any smartphone phone apps.
Personally I am online at least 95% of the time and on balance I feel that being digital free for much of the remaining 5% is good for the soul.
Moreover, although GTDNext is one of the best GTD applications, in my opinion nobody anywhere has written a really good GTD app yet no matter how much money you want to pay.
So my firm vote would be to focus on getting GTDNext's web application REALLY good before diverting precious resources to smartphone apps. And although GTDNext is good, just like all its competitors, it ain't there yet.