Axis is basically a servlet, so you can get to the HTTP header information. From inside your Axis SOAP service, you can get the MessageContext from Axis and then get the HttpServletRequest from that context. From the HttpServletRequest you can ask for the User-Agent.

MessageContext msgctx = AxisEngine.getCurrentMessageContext();

HttpServletRequest req = (HttpServletRequest) msgctx.getProperty(HTTPConstants.MC_HTTP_SERVLETREQUEST);

String userAgent = req.getHeader("User-Agent");