The following frequencies are used to transmit ACARS data to and from the aircraft:

Frequency in Mhz

131.550	Primary Channel worldwide
130.025	Secondary channel for USA and Canada
129.125	Additional channel for USA & Canada
130.450	Additional channel for USA & Canada
131.125	Additional channel for USA
136.700	Additional channel for USA
136.800	Additional channel for USA
131.725	Primary channel in Europe
131.525	European secondary
131.475	Air Canada company channel
131.450	Primary channel for Japan
136.900	European secondary
136.925	ARINC European Channel
136.85	SITA Canadian Frequency

Notes:

1/ 130.45 appears to have taken over as the major frequency for US domestic flights between major US airports. 130.025 now has mostly traffic originating/terminating in secondary airports PLUS an increasing number of international flights for ARINC customers.

2/ Although 131.55 is the primary channel in the U.S., several airports such as Chicago and Boston have noted more traffic on the secondary frequencies of 130.025 and 130.45.

3/ The Air Canada channel is only used in Canada. Recently activity has ceased on this channel and it may now be decommissioned. 

4/ 136.925 is a new frequency in Europe. It has been monitored mostly in the London UK area. It is an ARINC channel (verified by all messages being ACARS mode 2) and is used by those airlines who have signed up with ARINC as the exclusive provider. Aircraft already registered with SITA continue to appear on the SITA frequencies for now. Some of this traffic does appear on the SITA freqs but only very occasionally.

5/ 131.125 and 136.800 are new US frequencies that have been noted in the Chicago and New York areas. 131.125 appears to be a major ground frequency in the New York area. 

6/ 136.85 is a new Canadian frequency that has been noted in use in the Toronto area.