I have gathered this reference information for my needs and would like to share it for the benefit of others as well.

Zoom in on this article to view additional information. If you can read this text, then you are already zoomed in on this article.

Notes:

1. Extelcom (Express Telecom) was assigned the area codes 973 and 974 (presently not in use).
2. Globe area codes are: 905, 906, 915, 916, 917, 926, 927 and 935.
3. Globe Handyphone uses the area codes 905, 906, 915, 916, 917, 926 and 927. The 916, 905, 906 and 926 area codes are shared with Touch Mobile and 915 was formerly the area code of Islacom until the successful merger of Globe and Islacom.
4. Members of the Asia Mobility Initiative
   Celcom · DTAC · Idea cellular · Excelcomindo · MobileOne · Sun Cellular · Telstra
5. Members of the Bridge Alliance:
   Advanced Info Service · Bharti Airtel · Hong Kong CSL · CTM · Globe Telecom
   Maxis Communications · Optus · Singapore Telecommunications · SK Telecom · Taiwan Mobile · Telkomsel
6. Members of the Conexus Mobile Alliance:
   Bharat Sanchar Nigam Limited · FarEasTone · Hutchison Telecommunications International Limited · Indosat · KTF · Mahanagar Telephone Nigam Limited
   NTT docomo · Smart Communications · StarHub · True Move
7. Piltel uses the 912 area code for its AMPS/CDMA service. However, it is now used for Talk N Text. Pilipino Telephone also uses some of Smart Communications' area code assignments for its GSM services due to a facilities-sharing agreement.
8. Red Mobile is assigned the area code 938 in the Philippine telephone numbering plan. It previously used the area code 999 when it was still branded as ümobile and 989 when CURE was still independent.
9. Smart uses the area codes 907, 908, 909, 910, 912, 918, 919, 920, 921, 928 and 929.
10. Sun Cellular has been assigned the access codes 922 and 923.

Source: Wikipedia.Org