The cost statement was only considering the cost of your 24 LS lines vs. what a PRI from a CLEC would be. Not even considering your internet access fees, or shared T1 voice/data setup you had before..

PRI can get down in the $2xx/month range. 24 LS lines in my area at business rates would be something over $1000/month. Unless the vendors in your area are very inverted, you get all your features back with much less cost to ditch the 24 LS lines and go PRI from a CLEC. The ILEC cost case would be much closer, but the ILEC in my area would still be $150 cheaper for PRI vs. 24 LS lines. Seems like a nobrainer to me. Get all your features back, pay much less cost.

And FWIW: age doesn't matter much with phone systems. Some of these ancient hardware still have features the pure VOIP people are still wishing for..