Importing SMS and Call Log is an important feature for people coming from Android IMHO.

There are some tools enabling backup/restore of SMS and Call log to/from IMAP on Android. Check https://search.f-droid.org/?q=sms+backup&lang=en for instance.

Any idea how difficult it would be to implement that for UBports?

That would also offer a backup/restore solution for such data.

Even Nextcloud offer such feature (at least for SMS) : https://apps.nextcloud.com/apps/ocsms

Any idea where to add the feature request?