Prior to the introduction of the Missal of Pope Paul VI (popularly known as the "Novus Ordo" or "Forma Ordinaria" / Ordinary Form of the Roman Rite) in late 1969, the Roman Rite had the practice of veiling all (or most) of the crosses and images in churches during "Passiontide", which began with the Fifth Sunday of Lent (known in the Roman Rite as "Passion Sunday" until 1960 and as the "First Sunday of the Passion" from 1960 until 1969) and ended with Holy Saturday. This practice is still retained in many churches abroad (even those that use the Missal of Paul VI exclusively), as well as in the churches and oratories where the pre-Conciliar Roman Rite is followed. It is not required, but encouraged.
In the Philippines, at least in my experience, churches in the Metro Manila area normally veil their images only beginning with Palm Sunday. Some do so only for the Triduum, and I've gone to one major parish (which I shall not name here, out of charity) where the veils are used only on Good Friday. I've also heard from a number of friends that some Metro Manila parishes never veil their images at any time during Passiontide. On the other hand, some parishes veil their images as early as Ash Wednesday.
At any rate, there are at least two cathedrals in Metro Manila that follow the Roman Rite's historic tradition in this regard, namely, the Immaculate Conception Cathedral of the Diocese of Pasig and the San Roque Cathedral of the Diocese of Caloocan, which have veiled their images since this past Sunday (March 25, the Fifth Sunday of Lent):
Immaculate Conception Cathedral of the Diocese of Pasig
San Roque Cathedral of the Diocese of Caloocan
(H/t to Kristoffer Balazuela for the picture of Immaculate Conception Cathedral and to Noah Acha for the picture of San Roque Cathedral.)
Observation # 1 (March 31, 2012): Today I visited 7 churches in central Batangas. None had veiled images.
Observation #2 (April 5, 2012): According to a friend of mine, the Cathedral of the Diocese of San Pablo and the Catholic parish in Los Banos veiled their images today, Holy Thursday.