You can store the entry number as part of the serials. The way the other LG
phones work is that each entry has two serial numbers which are equal and never
change for that entry. Every time you create a new entry, a new serial is allocated
(the new serial being an ever increasing number).

When writing out to the phone, the existing entries and their serials are
read, and the entries being written out are matched to those. The
software inside the phone maintains the speed dial pointers correctly.

Roger