I'm a bit confused here too and would like to see us come up with a set of answers to the same list of questions for each vendor and product in the vendor's line, e.g. T1 vs T4 vs T7
Product
Product monthly charges
Central Station additional monthly charges
Primary or secondary connection
Phone Line fault monitoring
Different folks will have different needs. Some will want to optimize for lowest ongoing cost, some for lowest initial cost, some for use as a primary/only mode of communication, some only for backup.
Hopefully we can compile this and provide some useful info for all.