[jerseygirl]

Identical except for the last 4 digits. I wonder what that could mean.....same plan different location?

[callmejoe]

Actually, the four alphanumeric strings are identical except for all but the last digit in each sequence:

5-6-8-1

5+6=11
8=1=9

Which is consistent with the text. And serves as a "numerical suffix" for "723".

And as you pointed out, the only internally repeating sequence within the common string is "723"

If you can relate "4515 sb" to the above (4505, 4506, 4508, and 4501), then you have something . . .