I worked at Deltathree full-time (More than 3 years)
Some of the people who worked there were awesome. Unfortunately they tended to have relatively little weight.
Like I said - incompetent management with no vision. Sales and marketing people would bring deals to the table to be shot down for "resources" concerns. Deltathree could easily have been the next Skype or at least Vonage but consistently refused to invest.
Advice to Management
Focus on rewarding performers; deltathree let a lot of good people walk away for completely avoidable reasons.
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