Re: How to integrate 3cx in a hotel already using hard phone
3CX would replace perfectly existing PBX in hotel environment.
Hotel module (with or without PMS integration) would be valuable in most cases.
Regarding hardware, 3CX is not manufacturing any hardware, you need to buy a PC server with Windows OS (I would recommend a bundle from HP / IBM / Dell with MS 2008R2 Foundation as very good price/performance option).
Second you need to buy the appropriate licenses from 3CX partner, including probably hotel module.
Third, if you need to keep existing analog phones, you need to buy VoIP adapters (gateways). Grandstream GXW-4024 is a good option (24 FXS port 1U rack-mount is sold for about $ 700.- in Europe). Of course you will need some SIP phones (to replace any proprietary from the old PBX) -- for hotel management, reception, etc. The choice of available phones is big (Cisco/Linksys, YeaLink, etc.). I'm quite satisfied with recent Panasonic KX-UT series, nevertheless they are not officially supported by 3CX, but you have simple 1 or 2 key touch blind and attended transfer, conference, call pickip, etc., which usually are more complicated in other brands.
Regards