SMS center  by itself is a software  on a high spec server but it can be a regular box. its consults HLR and VLR (both are database) for recipient info and communicates with MSC for delivery of the msg. note that MSC here do need a specialized HW.

SMSC obviously should also support SS7, IP and other sms  protocols

with Kannel you don't seems to need specialized hw other than a high spec server, I guess if you do not have connection with smsc of your operator, Kannel will also provides that (I was doing some trial with Kannel over a year ago) and if that's the case the center number should be places on the SIM card as an alternative to subscribers default operator smsc#