Is it possible to optimize T-carriers for Transmission of Bursty Data?

I was going through the disadvantages of X.25 and one of the disadvantages was X.25 doesn't support bursty data.

Basically, bursty data are the data that require long connect times but low data volumes. Eg-: data traffic/internet traffic.

Quoting from Fourouozan book-:

T1 and T3 lines assume that the user has fixed data rate all the time.

For eg-: A t1 line is designed for a user who wants to use the line at a constant 1.544 Mbps. But, today users want to send bursty data.

i.e

Say we have a time interval of 10 seconds.

User wants to send-:

1) 6Mbps for 2 secs.

2) 0 Mbps for 7 secs.

3) 3.44 Mbps for 1s

Although it is basically, 1.544 Mbps(when averaged dividing with 10 seconds). But, T1 line cannot accept this type of demand because it is designed for a fixed data rate, not bursty data.

My question-:

a) So, can we use T-carriers for bursty data?

b) And does frame relay uses T-carrier? What else does it uses?

c) What was the last technology to use T-carrier?