This thread makes very interesting reading for me, as DS1 who is now 5 1/2 having been completely non-verbal before (he never had speech so didn't regress, iyswim) has started vocalising an awful lot in the last few months.
He still has hardly any 'true' speech, apart from the odd 'tickle' request when I am tickling him and he wants more and his speech is very unclear (its hard to explain but it is like he speaks in the right tune but doesn't know all the lyrics).
It also seems as if he is scared of his own voice, as he speaks very quietly and if you try to sing along with him, he stops and listens to you, rather than both singing together.
On the other hand though, if he is alone listening to the radio, I will often hear him singing along really loudly and he chatters endlessly to himself (albeit in his own language) in his bedroom at night. So it is almost as if he is shy of others hearing his voice.
Despite this and the fact that nearly all his speech is echolia, it is just so wonderful to hear his voice.
As he is so good at repeating adverts from the tv or radio, I cheated a bit yesterday and got him to say 'I love you' by adding '.com' on the end. I could spend hours saying 'I love you, I love you, DS1 say I love you' to no avail, but I only had to say 'I love you.com' (in a television jingle type fashion) once and he repeated it straight away.
Now I know this isn't true communication, but it was so nice to hear him say the words I never thought I would, although DH still thinks I am slightly mad.
I am hoping though that with persistance and using PECS to help label things that his speech may develop from simple echolia to some 'true language' i.e being able to label and request things he wants.
Although I am under no illusion that this may never happen, I also thought 6 months ago that I would never hear his voice, so there is always hope.
I agree with what others have said in that his lack of speech isn't as much of a problem as his behaviour/sensory/obsession issues are. Although it took us a while to realise this.