At this time, IP addresses of endpoints that can be accessed from SORACOM Air for such as Unified Endpoint and SORACOM Harvest are fixed regardless of the source device. You can check it with the following command.
nslookup uni.soracom.io
nslookup harvest.soracom.io
These addresses have not changed since the various endpoints were published, but they may change in the future. Please be careful when considering access by IP address for the purpose of reducing the amount of data communication that occurs during name resolution.