VBA Novice

Using VBA I want to know what Account code was last iputted (used) in a
given sequence within a column so the user know the next number to use (Users
are inputting via userforms so cannot see the spreadsheet.

Therefore if column A as codes SAT1, SAT2, SAT3 etc I want to able via a
msgbx to notify the users that SAT3 was the last Account code to be used and
therefore user SAT4 should be used next.

Obviously this will only be used when the user hits a command button titled
next availble account.

Many thanks

M