In order to use SIP trunking reliably and effectively, several components are necessary.
An IP PBX capable of SIP protocols will be required. 3CX, eMetrotel, Asterix are some of the available platforms. These platforms can either be installed on-site (at your office) or hosted in a cloud environment. Traditional phone systems always had an on-site system such as Nortel, Panasonic, etc. IP PBX platforms can be hosted for you in a cloud environment, eliminating the need for an on-site system as well as saving hardware costs.
IP phones are also required. Some of the more commonly used IP phones are Cisco, Yealink, Grandstream, etc. These IP phones will connect to either your on-site IP PBX or to a cloud PBX.
Finally a stable internet connection will be necessary. Ultimately the reliability of your phone system and SIP trunking will depend on your internet quality and your SIP trunking service provider.