Do you have to have a 'Voice' modem to be able to use it as an answerphone?

[cattz@xxxxxxxxxxxx]

Can I use one of these  
http://www.usr-emea.com/support/s-prod-template.asp?loc=emea&prod=5630 as
an answerphone. It dosen't say specifically that it is a 'Voice' modem. Do
I have to have a 'Voice' modem to use vgetty and VOCP to make an
answerphone service? Everything I've read seems rather vague. Do 'Voice'
modems just have higher quaility audio compression options or something
like that?