Well Hardware based solutions are the best but for starters and people with good linux skills ill still go for asterisk.
People lik u dont know what is carrier grade Voip equipment on the other hand some companies like ours hav our own equipment which include softswitches gw and gk and abt 100 e1s. I used Five9 in islamabad long time back i was also among the few at that time. Since than i hav been working on diff solutions and beleive me if ure a Telco lik us or u know some one who will giv u good quality outbound mins asterisk is the best thing. We are having some issues with busy tones and answering machines but inshah allah we will get thing sorted in a month or so.