Montano-
For being a small service with very few users Viatalk has been having lots of problems reported on dslreports as of late.
BTW, Viatalk is definitely more expensive than SR and the yearly rate comes only with a 50% money back guarantee in case you want to cancel. SR gives all the money back.
Let's not start with the features here. SR has about double the features Viatalk has at a better price. And, btw, there is also CALLER ID WITH NAME, also voicemail to email, but SR also has voicemail notifications galore, voicemail screener with intercept, etc.
Big question: Why would one want to STAY AWAY from trying this? Equipment is free. Shipping is free. There is no setup cost, no penalty if you cancel, full refund. PLUS you get to keep a $65 phone system for your troubles. There is a 31 day trial during which you can call anywhere in the world, and if you don't like it you cancel before the 31 days are up and owe nothing. No better way to try if this works for you.