I own an African Gray Congo Parrot and can attest to the intelligence of these birds.
Mine will call out names, imitate car sounds as well as electronic devices. She loves to say her own name and will curse probably better than most of the people on this website.
She also seems to understand to a very minimal extent of context to conversation.
There's just something about having the following conversation with a pet bird that you can think back on and laugh about:
Gabby:"Night Night!"
Myself:"Night Gabby!"
Gabby:"Ya ****in' bitch! HAW HAW HAW HAW"