Depends who is calling. I have caller id.

1) 1-800 or other garbage number: My computer automatically ignores and/or hangs up the call for me (yay phonetray!)

2) A name I don't recognize: I let it ring to voice mail.

3) Doctor/Dentist/other business: Hello

4) Someone I know: Hi <first name>.

5) My wife: (depends on my mood)

    - Hi lover.

    - What's up buttercup?

    - Yessss??

    - Joey's pizza....  ... haha :)

In Taiwan , we said :喂 (wei) (( hello

If the call comes from I don't know, I just say my last name. If I know the person who's calling me, I answer the phone by simply saying "Ja?" ("Yes?").

Come to think of it, I never say "Hallo".