I find that if I minimize headspace in the bottle most of my beers will carbonate sans priming sugar. It is sort of hit and miss but works most of the time. That said I've made some sweet bottle bombs by cutting it too close. Be careful.
I do it to retain some samples when most of the batch is going into the keg. If I'm bottling the whole thing, priming sugar is the way to go IMHO. Far easier to get repeatable results.
I have done a few from the tap too. It seems to work, but I always drink them almost immediately (like taking some bombers to a BBQ). YMMV.