My preferred terminal emulator is
Term which should run OK on the A2000; there's little you can't do with it. The earlier version Term v3.4 is better for low end unexpanded Amigas.
The internal serial port can be accessed with serial.device and is unit number 0.
I used to use a packet radio modem on an A600 for sending 1200 baud data over radio networks, but forget what software I used. Obviously you need a bit more than just Term for this as something needs to operate TX key/PTT, etc. I've still got the config for
AmigaTNC so must have used that at some point. I've also got AmiCom, Packet-Point and ProfiPacket here so probably used one of those. They're all available from Aminet.
