Systems/methods of bandwidth variability in cellular communications

A first device that is configured to perform operations comprising:

• responsive to information received from a second device, establishing at least three transmit modes comprising at least three respective air interfaces any two of which comprise a physical layer variant relative to one another;
• and
• storing at the first device the at least three transmit modes;
• then
• communicating with the second device using a first transmit mode of said at least three transmit modes that are established and stored;
• at any given time, while communicating with the second device, using at most one transmit mode of said at least three transmit modes that are established and stored;
• and
• selecting and using a second transmit mode of said at least three transmit modes that are established and stored responsive to:
• (i) a parameter associated with data that is to be transmitted, or
• (ii) an index received from the second device, comprising two bits of information;
• wherein said parameter associated with data that is to be transmitted comprises a value of data, a quality-of-service, a size of data, a velocity, an interference level, a bit-error-rate, a data rate, a time-of-day, a security/privacy concern, a location of the second device or a distance between the first device and the second device.