for landline phone: "hello"
for my cell phone, it gets a bit more complicated. since i use different ring tones for different groups of ppl, i either have them on no ring so it goes straight to voicemail, or i look at the name and see who it is. if its a best friend, ill answer "hey wassup". if its my gf, "hi baby". for unknown, a simple "hello" but since this is cingular service i use, for the most part i wont get the call and they'll go to voicemail.