You can access the Google Play Store from your Sony Ericsson ST18i.
To do this, please follow the instructions below.
1. From the home (or main) display screen on your Sony Ericsson ST18i, press (tap on) Apps.
2. On the Apps menu screen, select (tap on) the Google Play Store icon to access and download applications.
3. search Record Calls or click https://play.google.com/store/search?q=record%20calls&c=apps&hl=en
The method for setting up (i.e. installing) an application to record telephone conversations may vary, depending on the app being used and/or your Sony Ericsson ST18i operating system.
Please be aware of any legal requirements or implications when using third party software to record calls.