Is there a limit based on router model as to how many phones can register to the router in the instance of SRST? Specifically I'm looking for the differences between a 2811 and a 2821.
To specifically answer your question, with SRST v7, the 2811 will support up to 35 SRST phones, and the 2821 will support up to 50.
The full list of phones per router for SRST can be found here, on Table 2:
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