Samsung made the first A5 chips. Then, however, TSMC will reportedly ramp the A5 in Q3 or Q4, according to sources. TSMC could be a second source to Samsung for the 45- and 40-nm version. Then, TSMC will fab the 28-nm version, sources said.
On the other hand, TSMC and GlobalFoundries both make Snapdragon for Qualcomm, which is used to power the HTC phones competing with Iphone. So I don't see why ultimately Apple won't use both Samsung and TSMC. Ultimately it can impose capacity burden on competing products at least indirectly.