you might want to point out to them that a 2500 set is also very durable and is just the TT version of the 500 (rotary dial) they are probably planning to use
the problem i see is that so many things outide the phone system will not recognize pulses ,voice mail , banking , beepers ect ect be sure you point this out to them and that they understand that the innablity to use these functions is out of your hands