I have heard (not confirmed) of the following story: There was no "ka" sound in Mandarin, and 卡 was only pronounced as qia3. In southern Chinese, 卡 is pronounced "ka" (consonant "k" in southern Chinese is often "q" in Mandarin) and people used 卡ka to transliterate foreign words. And gradually the "ka" sound became popular also in Mandarin.
If you look up in a dictionary, it is true that there are very few characters with the sounds "ka1" "ka2" "ka3" "ka4" (mostly just dialectal words, interjections and transliterations). And in 《现代汉语词典》, there are 5 meanings of 卡ka3: 1. 卡路里的简称 2. 卡片 3. 磁卡 4. 录音机上放置盒式磁带的仓室装置 5. 卡车. So if you want to follow this dictionary, it is true that 卡ka3 is mostly used for translations, and you should use qia3 here.
But in real life, I agree with Skatinginbc, both qia3 and ka3 are OK. Actually I don't distinguish the meanings of two sounds clearly (except in the translations only 卡 is possible).
I do clearly distinguish their meanings. There would be loss of intelligibility for me if one pronounces 卡脖子 (qia3) as ka3. I honestly would not know what 卡(ka3)脖子 is supposed to mean. Also, 卡子 (qia3) = 夾子 (夾物的器具). If I hear 卡子 (ka3), I would imagine it is some sort of card or blockage.
I have another question. My friend told me today that 关卡 should be pronounced guānqiǎ but the dictionary I use has the pronunciation guānkǎ. Are both of these pronunciations common for this word? Which one would you recommend?