1/What kind of protocol is your 1800 system supporting? If it is still A/B, I don't think that DT292 support it.
A)The 1800 is GAP
2/Even if DT292 support A/B protocol, MD support GAP/CAP and both are incompatible.
A)Not applicable
4/At last; integrated mobility is supposed to replace 1800 systems; I don't see any advantage to keep it as there is no more support on that product.
A/ We use the 1800 for a dect based duress system, we switched from the MD because the ESS module built by ASCOM-Nira was only supported on the 1800 not the MD, and we needed the ESS module to do a broadcast SMS message to the 9d24 protector handsets