SMSC and MVNO

Some MVNOs have access to IN capabilities, some more still have access to the SMSC. So here's a recipe to maybe cash in on the operators SMS revenue.
First, take a large spoonful of SMSC access for your subscribers
Ensure you have a good GPRS data cost negotiated with the operator,
Next, reroute all incoming SMS over an instant messenger provisioned to your customers phones. When your customer replies to the IM, route it back to the relevant operator network via the best interconnect route.
SMS within your own network can be near free, SMS to external networks can bypass your agreement with the host operator, allowing you to drive the prices down by negotiating your own interconnect deals.
Then again, with most operators offering hundreds of free SMS per month to get contracts, it might not be worth the trouble!