voip router or adaptor

hi.. I use Ekida on Linux.. Its just a software for VoIP communication where you can set up more accounts but I dont like to have the computer still on so I just decided to find something like a router or adaptor which is able to manage more accounts together. I just wonder if any can be found but I say there must be one somewhere because these days if you have a mobile phones using two sim cards where is possible to choose which sim card to make a call .. so why not have a voip device for more than one SIP account. Otherwise I would have to find a someone who is able to change the software inside these devices. I would say the choosing the account should be by pressing a number on the phone - for example 'number one' choose VoIPbuster.com and 'number two' BLABLA and after dialing international format number...or in different way... ..easy! Why I am not able to find any.. So do you know any device? Thx.. Tom