WAP vs. SMS

We are a dispatch software for a verticle market. We can now send calls to pagers(one way) or two way to MDT’s such as @Road. We want to develop two way (return can messages or numeric values) via cell phone and Nextel. We have been getting mixed messages as to the best solution WAP or SMS.
The one important aspect is it needs to be quick 30sec to a min or so. What is your opinion?