As a SIP or VoIP service provider you will require an IP telephone handset to make calls on the Tel2 network. Commonly used handsets are those by Yealink, Polycom and Cisco/Linksys.
You can connect a traditional analogue handset to our service but you will need something called an Analogue Telephone Adapter (ATA) first to convert the voice traffic to digital and the SIP protocol. There are various options for ATA's too such as Cisco SPA112 and SPA122 and many others. Contact firstname.lastname@example.org if you need more assistance in choosing a handset or gateway device.