Am I missing something? I use Handcent for sms both incoming and outgoing they go through Google Voice and are instant. Is this not normal am I missing something?
Check your txt usage. If those messages are counting as SMS in your plan, it's not going through Google Voice completely.
More here: http://www.google.com/support/forum/p/voice/thread?tid=19f739f259f48929&hl=en