Austria has three mobile network operators: Drei (3), T-mobile and A1, which operate on the standard European frequency bands: 800, 900, 1800, 2100 and 2600MHz.
800MHz (Band 20) FDD

800MHz Band 20 LTE 4G in Austria by A1 and T-Mobile: 20MHz A1 EARFCN 62560, 10MHz T-Mobile EARFCN 6400.
900MHz (Band 8 FDD)

All three operators have spectrum in this band. A1 has G09 and UARFCN 3087, 3 with G09 either side of 3MHz L09 EARFCN 3632 and T-Mobile finish with G09 and UARFCN 3087.
1800MHz (Band 3 FDD)

All three operators have spectrum in this band. T-Mobile operates 20MHz L18 EARFCN 1300, 3 has G18 and 15MHz L18 EARFCN 1525. A1 has two L18 carriers for 35MHz: EARFCN 1700 and 1875.
2100MHz (Band 1 FDD)

All three operators have spectrum in this band. A1 has four U21 carriers: UARFCN 10564, 10588, 10613, 10637. 3 and T-Mobile split the spectrum between UMTS and LTE: 3 U21 10662, 10687, L21 10MHz EARFCN 372; T-Mobile L21 EARFCN 497, U21 UARFCN 10836.
2600MHz (Band 7 FDD)

All operators use this band: A1 EARFCN 2850, T-Mobile EARFCN 3050, 3AT EARFCN 3350.
2600MHz (Band 38 TDD)

3 EARFCN 37900.
Screenshots (2016)
Drei (3) AT.

Drei AT B8 4G speedtest showing 3MHz paired Bandwidth on Drei AT.

Drei AT Band 7 speedtest demonstrating the 20MHz paired carrier.

Carrier aggregation (CA) on Band 3 (15MHz) and Band 1 (10MHz) on Drei AT. Sometimes 20MHz is used on B3.

A speedtest of the Band 3 and Band 1 aggregation.
A1 Telecom Austria

A1 Austria has a 20MHz carrier on Band 20, capable of providing very good speeds even in slightly sub optimal conditions.

Their other standard layer is B7 20MHz.
T-Mobile AT

Band 20 and Band 3 CA on T-Mobile AT.