Every phone in the United States comes with something called a Ringer Equivalence Number or REN. Most other countries have some similar code. According to Wikipedia:
The total REN for a subscriber’s line is simply the sum of the RENs of all devices connected to the line; this number expresses the overall loading effect of the subscriber’s equipment on the central office ringing current generator. The local telephone company usually sets a limit on the total REN, typically 5 or less.
Basically, it means that some phones with higher REN’s use some of the electricity in the line to ring your phones. If the amount of juice needed to ring your all your phones exceeds the amount of juice available, your phones won’t ring. Before we had magicJack plus, we had an AT&T line. On this line we had an AT&T ‘trimline’ phone, a General Electric ‘big button’ phone and a panasonic cordless with several satellite phones. I originally hooked up all our old phones to the magicJack line, only to find none of the phones would ring.
It should also be noted that REN comes in two flavors: REN “A” and REN “B”. So if you see a REN of 1.0B or 0.1B, no you’re not misreading at as 0.08 — it really is a B.
MagicJack has a maximum REN load too. Depending on the lot your magicJack or magicJack plus was made in, your device may have a load of as little s 2.0 to as much as 3.0.
I looked on the back of our phones and found the numbers for all our phones:
|AT&T corded Trimline||1.9B|
|GE corded trimline||1.0B|
|Panasonic cordless with 4 satellite cordless phones:||.01|
|Total REN Load||3.0|
After recognizing this, the problem simply became figuring out which phones I prefer to keep and whether to buy new phones, most of which have ridiculously low REN’s. We dumped all the phones except the panasonic set and bought a corded GE big button phone with caller ID that I got at a yard sale for a couple dollars. I also found a cool cordless Columbo phone that had REN of 0.0B at RadioShack that we added and also use as our travel phone when we take the majicJack with us.
The REN can be found on the back of your phone. Here’s an example: