Using soap.asmx should work fine. It is a standard SOAP service. You should be able to discover the services using the typical soap.asmx?wsdl request. Here is an example: http://demo.splendidcrm.com/soap.asmx?wsdl
The API for SplendidCRM is identical to that of SugarCRM, with the exception of the file name ending in ASMX.