LOL. You have just activated a half-year old topic.
VOIP is very reliable and I'm using it quite often. I have not experienced any problems yet.
I'm using Skype and another SIP account (access via Nimbuzz) and it is more than satisfactory.
However, the direct clients for S60v5 would make some improvement in call quality. Hopefully, they will be developed soon (I should send an email to them).