At the time (2019) of writing this response there has been a lot of vendor consolidation.
In the past the following were vendors that could deliver Time-Space-Time Stored Program
Control (TST SPC) switches: GPT (GEC Plessey Telecoms), Ericsson, Nokia, Alcatel, Lucent, STC, Nortel, Motorola, Phillips, ITT, Siemens, Marconi, etc..
If we fast forward to 2019 we now have: Ericsson, Nokia (Alcatel/Lucent), Huawei, ZTE, Cisco, Jumiper and a number of IT / OSS / BSS (Operation and Business Support System) vendors that can deploy “Virtual Network Function(s)” towards a Cloud Data Center (GCP, AWS, etc..) environment.
Makes sense to have a mimimum of two vendors seleted for your “core” (2G / 3G / 4G / 5G / etc..) layer.
Consolidation is now a part of the Telecommunication landscape.