Aastra phones support Alert ringing. It uses a different table of tones than regular ringing.
Where are you getting this information? I had spent a lot of time researching this and the only thing I came up with was being able to change the cadence with the alert_info.
From the Aastra Admin Guide:
"Priority Alerting-
Priority alerting on the IP phones is a feature that allows incoming calls to trigger pre-defined ringing or call waiting alert tones. You can enable or disable priority alerting on the IP phone for the Asterisk, Broadworks, and Sylantro servers using the configuration files and the Aastra Web UI. Configuration of priority alerting is on a global-basis only.
Asterisk/Broadworks Servers -
The ring tone keywords that can display in the "Alert-Info" header for an Asterisk and Broadworks server are:
When the ring tone keywords appear in an "Alert-Info" header from an Asterisk or Broadworks server, the IP phone maps the keywords to the default ring tone patterns.
Asterisk/Broadworks Server
Ring Tone Keywords
Bellcore-dr2
Bellcore-dr3
Bellcore-dr4
Bellcore-dr5
Ring Tone Patterns -
A System Administrator can configure the ring tone adences if required, using the configuration files. The following table identifies the different Bellcore ring tone patterns and cadences.
As you can see... no tone variation. It is all in the Aastra Admin Guide.