[psim1]

No need to presume; the ITU-T standards are surprisingly readable!

https://www.itu.int/rec/T-REC-V.22-198811-I

For this older standard (1200 bps using FSK modulation) it does indeed use separate bands (from section 6.1):

On the general switched telephone network, the modem at the calling data station shall transmit in the low channel and receive in the high channel (call mode). The modem at the answering data station shall receive in the low channel and transmit in the high channel (answer mode).

The newer modem standards are far more sophisticated and I don't know anything about them. I picked this one because I had been working with V.22 in the past year.