On Windows I would use SoapUI, which can be run on Ubuntu either as a standalone application (see instructions on how in this question) or as an Eclipse plugin. Is there any other GUI available - perhaps something in a repository - for testing SOAP services?
You can still use SOAPUI
download the script from here and save it on the disk.
then from a terminal
Or if you don't like command you can do it graphically
right click on the downloaded file then properties and go permission tab and allow permission to execute as a program.
Once that is done double click on the .sh file and select 'Run in terminal' or Run
Then follow step by step instructions to finish the installation.
Membrane SOAP Client is a generic SOAP client written in Java. It provides a dynamic form generator for SOAP requests.
Also you can use jmeter a 100% pure Java application designed to load test functional behavior and measure performance. It was originally designed for testing Web Applications but has since expanded to other test functions. Jmeter is in the Ubuntu repositories.
Mooza is the best alternative for a soap client tool. This is a web application which can be easily deployed on Tomcat/JBoss/Jetty etc.