I'm on VM R200 unlimited sms's contract as well. Apart from my sms's being delivered a tad bit later, I'M RECEIVING SMS'S SENT TO ME 5 HOURS LATER. And then apart from that, the only reason I get the sms that was sent to me, was by sending out an sms, only to realise the timestamp is 5 huors earlier. Probably all sounds a bit confusing by the way I phrased that, just think of it as pinging a server and only getting a msg sent to you 5 hours earlier after you made a ping request.
I have had this problem ever since joining Virgin in Dec 07', about 70 - 80% of my virgin to virgin sms' are delayed. I send anywhere from 500 to 1000 sms's a month. And they are delayed anywhere from 10 min to a few hours, or sometimes they just never deliver. Their call centre is useless, they either don't understand, or eventually when i do get through to someone useful, they say i must record 5 instances of this happening and then call them back. Ofcourse when i call back, either i get through to the person that does not understand again, or I tell them about the 5 recorded occasions and they never call back! So when i follow up, they have no record of it. This has happened about 3 or 4 times now. Plus my phone is in for repairs now for the 5th time, but it has been different problems so they won't give me a new phone.
In fact the last time it went in for repairs they wanted my proof of purchase to prove it was still in the 2 year warranty, so I asked them how long my contract was, to which the answer was 2 years. So then I asked if the phone came with the contract, they said yes. But apparently they still needed proof otherwise I needed to pay the R890 or they would not return my phone!! Although when i said since they have no proof i took out the contract, i just wont pay next month, then magically the proof appeared on her computer that my contract was not yet up, therefore my phone still being in 2 year warranty!
Virgin mobile sucks @$$....fact! Pity their rates are so good though..
So anyways just waiting until December, then it's me, vodacom and my new iPhone

I would rather pay more for a reliable service and a better choice of phones.