ALE lets the radios in a network decide on the best frequency for operation. ALE can provide either a voice channel link, or a text data link for message traffic. From a pragmatic viewpoint, this would probably work best at a regional level. However, the range of frequencies involved would also support transcon operations. Its effectiveness will still be affected by the power levels and types of antennas used.
As I mentioned in 2004, there are ALE ready radios. However, as a rule they are expensive and scarce. They are not a practical option for MARS use.