anyone mind if i stick my voip in?

[AliceLost]

ok - xp pro, broadband conn & voip subscriber.

2 features vonage cant/wont gimme:
call blocking/filtering & caller id on my pc (nothing fancy, i just wanna block anons & have caller id displayed on my monitor same as on any phone)

i found there's a bunch of s/w out (cheap if not free) that can do these 2 things - all mention voip & all also require a dial-up modem.

WHY?

(my pc is built & ive always used dsl or cable - never a dial-up subscriber so never needed a 56k modem) what is it the dial-up modem can do that the cable modem (& voip adaptor) cant or isnt doing already?

and to make sure i stay confused, "everything" is digital these days anyway (like my phone for example - motorola md491 cordless digital expandable system so i only need the one jack) so what's still analog besides my voice speaking these words as i type them?!?

i have hens teeth i will trade for this knowledge (heh heh) or maybe i could just take someones word for it that i need a dial up modem & that's that - as long as modem recommendations (which ones & why those) are included...

THANK YOU!!!