# Building AWS Lambda functions for the Amazon Chime SDK PSTN audio service
<a name="writing-lambdas"></a>

**Note**  
Amazon Chime SDK SIP media applications will no longer be open to new customers starting October 29, 2026. If you would like to use SIP media applications, sign up prior to that date. Existing customers can continue to use the service as normal. For more information, see [Amazon Chime SDK SIP media applications availability change](https://docs.aws.amazon.com/chime-sdk/latest/ag/sip-applications-maintenance-mode.html).

The topics in this section explain how to build the AWS Lambda functions used by your PSTN audio service. 

**Topics**
+ [Understanding telephony events for Amazon Chime SDK PSTN audio service](pstn-invocations.md)
+ [Understanding Amazon Chime SDK PSTN audio service actions](about-actions.md)
+ [Learn about the telephony events that invoke AWS Lambda functions for the Amazon Chime SDK PSTN audio service](invoking-Lambda.md)
+ [Responding to invocations with action lists using the Amazon Chime SDK PSTN audio service](invoke-on-call-leg.md)
+ [Supported actions for the Amazon Chime SDK PSTN audio service](specify-actions.md)
+ [Using SIP headers in the Amazon Chime SDK PTSN audio service](sip-headers.md)
+ [Using call detail records in the Amazon Chime SDK PTSN audio service](attributes.md)
+ [Understanding timeouts and retries for the Amazon Chime SDK PTSN audio service](timeouts.md)
+ [Debugging and troubleshooting the Amazon Chime SDK PTSN audio service](debug-pstn.md)
+ [Understanding VoiceFocus for the Amazon Chime SDK PTSN audio service](voice-focus.md)
+ [Amazon Chime SDK PSTN audio service glossary](chm-dg-glossary.md)