Are you sending the photos directly from having taken them? Saved, or re-sent photos between Android and iPhone in either direction seem to sometimes have difficulty. There can also sometimes be difficulties if the group which photos are sent to includes both Android & iPhone users.
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We do both -- send directly taken and saved images. Oddly iPhone users in Canada (Calgary also Telus) and Ottawa can receive our MMS messages but both iPhone targets in the USA cannot receive our photos but we get theirs!! Must something to do with the Telus to US carrier transition?
Something else I noticed on the Telus messaging usage records for our account -- SMS text messages on our non-NA wide plan phone show up as $.40 each to 323 area code (LA) but an attempt to send a photo message to the same iPhone shows up in the record but with no attached charge. Looks like the MMS infrastructure is somehow aware that the photo message was not delivered.