today i had to install soap extension in my php, i have linux fedora and when i did my phpinfo() file i did not see soap in there. so if you have red hat distributions like fedora or centos for example, you can install it with yum simply by executing this command from the linux shell. installing soap is easy with linux, you must be logged in as root:

yum install php-soap


if you want to update soap:
yum upgrade php-soap


if you want to remove or uninstall soap:
yum remove php-soap


hope this helps.