You're not going to get a good answer to your question because you've provided absolutely no information such as your VoIP provider, VoIP hardware and EFTPOS terminal type. The only real answer to your question is "possibly".

Your best solution is to ask your VoIP provider if they support EFTPOS.

EFTPOS can work fine fine VoIP but it depends entitely on your VoIP provider and your hardware. Some old terminals are very fussy about VoIP connections and will fail unless a low pass filter is fitted to the FXS port.

With 99% of new terminals supporting IP it's a moot point anyway, IP EFTPOS should be your solution, not VoIP.

pankajbanga: Thanks for the answers , I haven't decided the provider yet , but will be using SPA2102 and most probably slingshot as provider.

If you have a DSL service for the VoIP just plug an IP EFTPOS to one port of the router and the SPA to the other port. Why complicate things with EFTPOS over VoIP if you can have it IP native?

Even if you save a few crumbs it will be a pain to support later.