It's always been difficult, if not impossible, to create a synthesized voice file suitable to upload to Second Life.
Now it is easy. Just navigate to http://secondlife.mitsi.com/cgi/send_smsxTTS.pl , enter any text, select the 44 Khz Resolution, and it the program will create a text to speech file for you, all ready to upload.
This system converts text to female or male speech. You may have to chop the resulting wave file into 10 seconds pieces and play it back with a script. The script is also available at http://secondlife.mitsi.com/cgi/llscript.plx?Category=Sound