Hello @MTayal
Skype4B on-premise will never leverage transport relays as far as I understand the technology which was introduced as Transport Relay for O365 and mainly with driver from new Microsoft Teams client.
S4B Online client still communicates first with media relay but that one forwards the request to TRAP (Transport relay) so I do believe that S4B Online users can benefit from new infrastructure for most reasonable routing of media. There are a few very nice blogs describing this. I found one article on Tom Talks, Stefano Ceruti Blog and also Microsoft Coffee in the Cloud Videos describes the overall flow of media.
