Castel SIP is an easy-to-use and intuitive SIP intercom softphone for Android devices. It allows users to make and receive audio and video calls from XELLIP IP intercom stations. With Castel SIP, communication and door opening become seamless, no matter where you are.

The app offers advanced calls management features such as call holding, call transferring, and audio conferencing (with server). It also provides an address book for easy access to contacts, as well as a call history for quick reference. Users can even record calls for future playback.

Castel SIP supports various audio codecs including G711 (ulaw, alaw), GSM, and G722, and video codecs such as VP8, H264, and H265. It also features echo cancellation and allows sound output through the speaker, hands-free, or Bluetooth. Additionally, it supports DTMF tones using in-band, SIP INFO, and RFC2833 protocols.

The app can work in standalone mode or with a Castel SIP server, either locally or hosted by Castel, and can be used over Wi-Fi or 3G/4G. It offers transport options like UDP, TCP, or TLS, ensuring interoperability with any audio/video SIP phone supporting the aforementioned codecs.

Please note that before using Castel SIP App, it's important to check your cellular operator's terms of agreement to ensure they allow SIP calls on their network.