I am not sure I understand your question, so I hope I answered it correctly.
If you would like to host a website for users to send SMS, you do not need a WAP Gateway. But, you will probably need service from an SMS Aggregator.
If you would like for mobile users to view your website, then you can host your site on any webserver and users can go from their home WAP Gateway to your webserver.
If you would like to allow users to send MMS from your website, you will need to contact your local carriers. They will have service aggrements for connecting to their MMSC. Or, there are a few MMS Aggregator companies (depending on your location in the world). Some SMS Aggregator companies are starting to move towards MMS services also.
Service varies from country to country, so do a search on the internet for "SMS Aggregator" or "MMS Aggregator" for your country or area of the world.