Hi splosher,
This can be done with the 'Sound Recorder'. The default recording device will probably be 'Microphone' and this will need changing to 'Stereo Mix'. To do this, click on the start orb and type 'Sound' into the search box and press enter/return. The main dialogue panel will appear. Select the 'Recording' tab.
Scroll down the list until you see 'Stereo Mix'. Ensure that this option is highlighted and then click on 'Properties'. The 'Stero Mix Properties' dialogue will open with the 'General' tab active.
On this page, use the dropdown box next to 'Device usage:' to select 'Use this device (enable)' and then click 'Apply'. Click on the 'Levels' tab.
Here you can set the recording level. I suggest 50, but you can set it to whatever you want. Click 'Apply' when you have finished and then click on the 'Advanced' tab.
Use the dropdown box under 'Default Format' to select the quality of the recording. Click on 'Apply' and then 'OK' to return to the main 'Recording' tab.
Click on 'Set Default' and then click 'OK' to close the 'Sound' dialogue panel.
To start recording, click on the start orb and type 'Sound Recorder' into the search box and press enter/return.
When you reach the section of your MP3 file that you wish to record, click 'Start Recording'.
Likewise, when you have finished recording, click on 'Stop Recording'. You will then be given the option to save the file generated. Note that it will be a '.wma' type file.
Check the phone manufacturer's website for details on how to transfer this file to your phone.