The OS constantly nags you if you're without a SIM card. You're either reminded you have no signal or you're reminded you're in airplane mode (The signal icon on the notification bar becomes useless. There are messages in the notification dropdown and on the lockscreen.)
If WiFi calling were native, support would be built in to turn off these reminders. Connectivity could be displayed where signal is, instead of adding another icon to the notification bar. The app could be moved to the system partition (Coming from a Nexus One, app space was hard to come by. GrooVe IP hates being a system app and you can't move it to the SD card w/o it not starting at startup).
I've bought GrooVe IP, I just feel like a native approach could work better.
