Hi - my dd is nearly 5 and just started school. She could name shapes, count and write her name at about the same age as your ds. They taught them the jolly phonics rhymes at nursery and that has continued at school. She's now obviously learning to read and what I've really noticed is (and I'm not particularly thick and have learned to read myself many years ago ) that there is a world of difference between knowing the letter sounds and actually reading.
DD sounds the letters out and then says the word and that is great for lots of words ... cat, dog, big, has, can, on, etc ... but not particularly helpful for the vast majority of them ... the, she, one, two, you, same, etc. So whilst I think the phonics are great, they do also need to learn the letter names as many this does help them with letter sounds too ... low, ate, high, boat, etc. And then there are all those words that just make no sense phonetically at all, that they just have to learn ... that's quite a lot for a not quite 3 year old to grasp, it's a lot for a not quite 5 year old to grasp. DD was reading a book last night and it had Poppy on every page. She'd sound it out, say it, and then the next page she'd have to do it all over again ... and she's doing well at school. She's obviously looking at the words almost letter by letter and not then looking at the whole thing. Which really brings me to the conclusion that we try to teach our children to read far too early!
So basically, I agree in keeping on encouraging, drawing, playing in a way that incorporates numbers, letters, words etc. I Spy is a great game for that ... you can start with "something the colour of ..." or "something the shape of ..." or "something that sounds like ..." if he's not quite ready for traditional I Spy.
That said, my niece was just super-bright and she could read by the time she got to school ... but her parents didn't do anything that you're not already doing and she just picked it up.
Sorry for v.long message and welcome to mumsnet!