No it's not. You're just reading it wrong. "Bob and Jane are here. They need the cell phones now."
I'm only guessing but the two sentences "They need THE cell phones now" and "They need cell phones now" have different meanings. In the first case, it sounds like they already own cell phones and they need them. In the second case it sounds like they need to go buy cell phones. That's my thought process for what it's worth.
You are absolutely right. However, it's my opinion that we don't have privy to the context of these statements. Until Duo provides context we just have to guess their thoughts. My question is how does one translate into Spanish "They need cell phones now.
I left out "the" and Duo said I needed the article "the." Maybe translating from English to Spanish may require certain articles. However, translating from Spanish to English does NOT require articles. Since we don't know if cell phones need to be purchased or if they already have cell phones then it's difficult for many to answer correctly.
The sentence here is talking about specific cell phones. You need the article in both languages. If it were "They need cell phones now" in English, it would be just as article-free in Spanish: "Necesitan celulares ahora."
Sam: I disagree. I have over 27 years experience in wireless telecommunications wit ALL the major US carriers (ATT Wireless, Verizon Wireless, Sprint and T Mobile and the term "cell telephone" is a common term as well. You can not be a native speaker or familiar with the industry.
Did I miss the note where this course is based on US English? You likely long ago learned that other countries speak English, and are thus native English speakers.
It is largely based on US English. However, English from other parts of the world, including Britain, should be accepted. So, if mobile isn't accepted, report it.
From the English course description pages (es, fr & de - i didn't bother to look beyond that):
On Duolingo, you'll learn American English, but you'll be understood in any English-speaking country.
Also, it only takes a cursory glance at spelling / word choices to see that American English is what's being used by Duo, though non-american spellings or words will generally be accepted. Report the sentence if it doesn't.
It's either "cellphones," perhaps "cell phones", or arguably "cellular telephones." Never have I seen or heard "cell telephones," and I'd have to disagree with you regarding being acceptable, as it doesn't sound right at all.