Oh ok. Not sure that smsgui can help you with that.
It seems like you need more than just a gateway. You need a provider who can do 'direct billing' or 'reverse billing sms'.
This will depend on whether your bill is a subscription and how they agree to the terms - online or through replying to an sms sent to them.
Another company that I came across a long time ago is 3bill (
http://www.3bill.com/mobilebilling.php)
They might have what you're looking for.
It's been sometime since I looked into this for myself. All that I can remember is that many providers will take 10-20% of the charge depending on contract. (eg/ if you bill the customer $10 by this method the provider can take about $2 depending).
Good Luck.
AFTER THOUGHT:
If for your business you're wanting people to text "WIN" to 80091 (just an example) then this type of thing usually always has set up costs, and they're pretty high. It involves buying or renting a short code and number. These charges are high because each of the phone networks charge for the shortcodes to be used on their network. You can usually save a bit of money by using a shared shortcode. eg/ If "WIN" is a shared short code on a premium sms number, you would ask people to text "WIN XXXX" to 80091 (where XXXX is a unique word)
I just added this bit because I'm not sure if you wanted to charge customers for something like a software download (what I was talking about earlier) or a ringtone subscription (my after thought).