NeoSpeech is a software vendor of a Text-To-Speech engine of a very decent quality. Also they offer a web service API with free basic membership. The basic account is able to create WAV files from your text, and NeoSpeech arbitrarily adds pieces of advertisements before and/or after your phrase.
Important! End your text phrase with a dot, otherwise the spoken phrase will sound unfinished.
After you register at their website, you get an Account ID and a login password. The rest is easy. The following example illustrate how to use their services from a Linux or Cygwin command line:
curl https://tts.neospeech.com/rest_1_1.php \ -d method=ConvertSimple \ -d 'email@example.com' \ -d accountId=ef******* \ -d loginKey=LoginKey \ -d loginPassword=5**************6 \ -d voice=TTS_JULIE_DB \ -d outputFormat=FORMAT_WAV \ -d sampleRate=8 \ -d text='Press One to answer the call.' # Output: # <response resultCode="0" resultString="success" # conversionNumber="3" status="Queued" statusCode="1"/> curl https://tts.neospeech.com/rest_1_1.php \ -d method=GetConversionStatus \ -d conversionNumber=3 \ -d 'firstname.lastname@example.org' \ -d accountId=ef******* \ -d loginKey=LoginKey \ -d loginPassword=5**************6 # Output: # <response resultCode="0" resultString="success" status="Completed" statusCode="4" # downloadUrl="https://tts.neospeech.com/audio/a.php/XXXXXXX/XXXXXXX/result_3.wav"/> curl -O https://tts.neospeech.com/audio/a.php/XXXXXXX/XXXXXXX/result_3.wav
The resulting result_3.wav file is a 8KHz WAV file can be edited in any sound editor (Audacity for example) and you get a nicely spoken phrase for your IVR application.
The paid account offers more goodies, like more granular control on pronunciation, and also it produces ad-free output.
UPD: make sure you read the NeoSpeech TOS and use your audio files accordingly.