Há um som de "i" em "I'll"(ail). Confira nestas boas ferramentas de pronúncia:Pronúncia de "I'll"Pronúncia de "I'll" - MacmillanPorém, existe algo interessante a ser considerado.
Da Wikipedia:Relaxed pronunciation
(also called condensed pronunciation or word slurs) is a phenomenon that happens when the syllables of common words are slurred together. It is almost always present in normal speech, in all natural languages but not in some constructed languages, such as Loglan or Lojban, which are designed so that all words are parsable.
" gets contracted to "I'll
" [aɪjəl], which in turn gets reduced to "all
" [ɑl] in relaxed pronunciation. E.g. I'll do it: [ˈɑl ˈduɪʔ(t)], all do it.Sobre "relaxed" pronunciation - Wikipedia