

Bandwidth is akin to number of lanes on an interstate, latency is how long it takes each car to go from point A to B (or X, or wherever you’re measuring to).
Technically, bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. It is typically measured in unit of hertz (so how “wide” is the signal) - in ye olden days the signal width corresponded to transmission capacity.
While latency is a measure of how long a specified bit of data took to transit a system, especially when compared against the “ideal” performance of the system.


To tack on to this:
SMS requires practically no transmission cost, as it is embedded in an unassigned portion of the frames being sent between the phone and tower - frames which are always being sent anyway for keep-alive, registration, etc. There’s some infrastructure required (SMS gateway, network to other cell companies) so it’s not completely a sunk cost for them.
MMS historically worked the same way, just the media was base-64 encoded, and required an http server to temporarily host the media files for the person you were sending to.
Begin the age of the smart phone and data plans - now MMS are sent via the data connection because it’s much faster and doesn’t consume voice channel time, leaving more voice channels available for voice calls.
Today SMS is still largely sent the old way, but with 4G/5G the connection is completely different (it doesn’t use the same framing), so effectively it’s being sent via the data connection.
Voice is generally no longer via a voice channel, but really VOIP - vendors have pushed for voice-over-data since the beginning of 4G (I think LTE doesn’t even have voice channels anymore, 5G definitely doesn’t - it’s all essentially VOIP).
This is all from memory, so may not be spot on.