You can upload a spreadsheet to the External Directory at Directory page of the Configure Utility. After apply the configuration, you will see them at each phone menu->Directory->Corporate Directory->External Directory. You can dial them from there by moving the cursor to the number and pressing dial softkey.
Speed Dialing (or Abbreviated Dialing) is a hugepain point on this system/ I've brought thsi up before but would appreciate if CISCO could consider an enhancement request to address.
Note today to dial a system speed dial (on a 525G2) you have to press three phone buttons just to be presented with a choice of numbers (Directory->Corporate Directory->External Directory + then scroll to the selected number.) At this point it's quicker to dial the number manually.
Suggestion is to dedicate an entire initial dialing digit only to speed dials. Meaning if you have a 3 digit system, dedicate maybe "4" as a speed dial designation. Then have a menu via the CISCO Web configuration utility whcih allows for programming of all speed dial numbers.
As an example, once programmed, dialing a local extension such as 4XX would then dial the associated external number.
401 might be directed to 9,214-555-1212, 432 might be directed to 8,312-555-1111. So in the case of a 3 digit system you would be able program 100 Speed Dial / Abbreviated numbers whcih could be dialed (must easier) from ANY phone (not just a 525G2) on thsi system.