Learn English – Pronunciation of “a” in “cat”

I'll and all are homophones in many dialects, including mine. In many other dialects, I'll, isle, and aisle are homophones. Generally, either of these pronunciations will apply. It seems that the first is more common in American dialects and that the second is more common in British dialects.

To summarize the responses in the comments:

In many dialects, both British and US, [ɫ], the ‘dark’ post-vocalic variant of the phoneme /l/ is reduced.

Following an unrounded vowel, it becomes a longish offglide [ʊː]:  standard [kɪɫ] (kill) becomes [kɪʊː].

Following a vowel which already has this offglide, it lengthens the offglide:  standard [kɔʊɫ] (coal) becomes [kɔʊː], standard [kaʊɫ] (cowl) becomes [kaʊː].

Following a rounded vowel, it may either reduce to an offglide [ʊː], often with some reduction of the base vowel for more contrast—standard [kɔɫ] (call) becomes [kəʊː] in my dialect—or it may simply lengthen the base vowel:  standard [kɔɫ] becomes [kɔː].

These changes are not affected by a following consonant, so standard [kɔʊɫd] (cold) becomes [kɔʊːd]. The only difference between cold and code, then, is that the [ʊ] piece is slightly longer with cold.

Note, however, that these changes do not take place (at least in my dialect) when phonemic /l/ is followed by a vowel, as in calling. In this case, /l/ becomes the beginning of the following syllable; in that syllable-initial context it loses its ‘darkness’ and is pronounced as [l]: ['kɔ⋅lɪŋ]