Actually, that's an interesting question. It could be argued that you're a cyborg once you have any implants, including the 90-years old granny with her artificial hip!
Or how about corrective eye surgery?
CP2020 played around with this question a bit (though not much more than SR).
However, given that cybernetics (IIRC) means the study of control-systems, I'd say that non-controlled implants, like the artificial hips, or bonelacing doesn't strictly speaking make you a cyborg. However any piece that's to do anything (at all!) on it's own, including moving, makes you a cyborg.
This means eyes, ears, arms, smartlinks and yes, certainly datajacks, chipjacks and their ilk.