Allah Ta`ala said: ‘’ ‘’The one who comes to witness the month (of Ramadhaan), then he should fast.’’ (2:185) Witnessing is to be present in that particular area.
أَنَّ ابْنَ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا قَالَ سَمِعْتُ رَسُولَ اللَّه صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ إِذَا رَأَيْتُمُوهُ فَصُومُوا وَإِذَا رَأَيْتُمُوهُ فَأَفْطِرُوا فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ بخاري
The beloved prophet Swalallahou Alaihi Wasallam said: ‘’Fast when you sight the moon. Do eid when you sight the moon. If you could not sight the moon, then complete 30 days of Shabaan.’’(Bukhari)
O Ummah of Rasouloullah SAW, the sunnah of Rasouloullah SAW is sufficient for us until the day of Qiyamah.
Read more on http://islam-qna.org/Articles.asp?QID=369&LN= that the differences of moon that the beloved prophet SAW left the ummah on that.
Bear witness that the islands of Indian ocean, South Africa, India, Pakistan and many other countries are still following this Sunnah.