I know in my rational mind that it’s “synced”, but half the time, I end up saying “sunc”. As in sink/sunk. Anyone else’s brain cross-wired like that? 
Headed out to spend the New Years weekend with my in laws in Eugene, OR. Hope everyone stays safe and happy!
Believe it or not, one of my co-workers googled and showed me this site, after I had said ‘sunc’d’ over the phone (I do tech support). So yes, there are other people out there who are just as ‘cross-wired’ as you are 😛
Things would have been much easier if people were using the correct verb: to synchronize. Then the past tense would be: synchornized. I wonder if the “verb” “to sync” even exist in the Oxford dictionary.
Like Andrew, I’m in tech support. Not only have I often heard ‘sync’-‘sank’-‘sunk’ for the truncated form of the verb ‘synchronize,’ but also ‘troubleshot’ as the unlikely, but entirely correct to my mind, past tense of ‘troubleshoot!’ Guy Deutcher, author of _The_Unfolding_of_Language_ wouldn’t bat an eye at this borrowing of tense forms from similar verbs. According to him, this is how it’s done — always has been. Cheers!
To say, “They synced their words together,” is absolutely ridiculous. Ditto for sunc or anthing like that. I agree with Pat. It is a shortened version of synchronized. So, use the whole word. This word may be a candidate for modification, like, synched, or like the treatment of picnic (picnicked) might be in order. Syncked? Synked? Nah. But not synced either. I’ll stick with synchronized.
HAHAHAHA, we are sitting here in Buffalo, NY talking about the different ways to say the way we sink out IPhones/Ipods/ your debate returned first on google search entitled “past tense of sync phone”.. Keep it living Derek Leibfried, Undergraduate in B.A Communications University at Buffalo. HOLLA