AusBonsai

Hi, does anyone know what this tree is? They line some streets in Adelaide, have a slight scent when first flowering, have rough old bark and smooth barked new growth with clusters of white blossoms.

Most likely a decorative Pear. P. calleryana or P. usuriensis.

Maybe an ornamental pear?

Oh nice! Thank you. Are they any good for bonsai? There's a branch overhanging our fence I could easily put a layer on...

Ornaments are generally decorative.

You should be able to find some threads on this site showing other pears used as bonsai. (search button top right)
Nice flowers but they don't seem to ramify particularly well so you'll need to pinch and prune well to get the best bonsai out of any pear. Like crab apples, sometimes the display of flowers can make up for (or distract the viewer from) the lack of structure in the tree.

Excellent. Thank you all!