With trademark infringement, I think that the point is "Where does it start causing confusion?"
Take your "jPhone" for instance: As long as the "j" was accentuated -- ALWAYS accentuated -- so that there was NO way that a cursory glance would not mistake it for an "i" -- a different font, colored a bright, screaming red where the rest of the logo is turquoise, the tail of the 'j' is made longer than usual... the possibilities are endless -- it might pass the "not likely to cause confusion in the general public" smell test.On the other hand, making the logo in a similar font to Apple's, in the same all-black, with the tail of the "j" shortened or otherwise de-emphasized (which is,itself,another judgement call -- when is something "too much"?) to lessen the difference between a "j"and an "i" then a case can be made that it DOESN'T pass that test.
xPhone, if made suitably visually distinctive, might pass the test... it might not. aPhone, all the rest... same thing -- maybe maybe not. Picking theone letter that MOST CLOSELY resembles the one that differentiates an "iPhone" from a "phone", however,is likely to be a bit whiffy on the smell-test
The real question,though,is -- in the case of someone wanting to enter a market that ALREADY has a competitor selling a well-known and popular product with an identifiable name -- why would one WANT to use a similar-sounding/similar-looking name if they're NOT hoping to ride on the coattails of that other product in the public mind? Remember that the term"iPhone" was not in common usage when Apple named their product. Once they DID bring the term into common usage, however, it became the responsibility of companies following on from there NOT to attempt to infringe -- just the same as it would be their responsibility not to name their mobile phone the "Galazy S", or the "Blackbury", or any number of OTHER "trivial variations to the generic term" that resemble products already on the market.
Interestingly -- to me, at least -- is; that, if I read aright, Apple maintains the sole right to the name iPhone for "computing devices", just not cellphones. Does this mean that the Brazilian company has to cripple their (otherwise,non-infringing) telephone so that it can't access the Google store or run non-phone applications? It seems to me that a case could be made that allowing it to run non-telephony-related apps would put it dangerously close to, if not INTO, the area of a "computing device".