Re: when can I have 'answerig machine' application?
Also, a problem with a device based "answering machine" app, you would miss calls and messages if you were out of service range, or your battery died, or the phone was otherwise unable to answer the call.
Voicemail (carrier side answering machine if you will), will take your calls even if your phone is dead or unreachable.
Talk to your carrier about setting up VoiceMail (it's included in ALL the prepaid and postpaid plans here in the USA), so I would guess it's included, or at least available, on all cellular plans.