Mavericks Messages problem sending message: "not registered with iMessage"

Question

I'm on MacBook Air(MBA) and recently installed Mavericks. I try sending a message from MBA MESSAGES to a person's cell phone number (they have an android phone). Their name appears in red and I get: "...is not registered with iMessage." So I was trying to read discussions in here and allot of them say Messages won't work unless a person has an Apple device- iphone, Mac, etc. I want to know if that is true or if there is any other way to send from the MBA a message to them? I also tried from Messages on MBA to their gmail address, which they use on their android cell phone, and get same error.
Is there anyway a non-apple person can "register with iMessage" if they have an android phone?
I know I can email them, but I wanted a fast way for emergency purposes to get a MESSAGE to them from my MBA. Sometimes they can't talk on phone at some times, but are allowed to get instant message for emergency where they work.

Answer 1

Hi,
You have to have otr get an AIM or AIM valid name.
AIM stands for Aol Instant Messenger.
Apple IDs issued by Apple (Those ending in @mac.com or iCloud issued @me.com and @icloud.com) are valid as AIM Screen Names if the password is kept to 16 characters or less. (this is an AIM server limit)
Apple made an Agreement with AOL over the use of names over 10 years ago.
The Original .Mac ID (@mac.com) could be paid for  or could be Trial Accounts.
Trial Accounts continued to work after the trial ran out. (i.e. the email stopped but the AIM Screen Name didn't).
The same was true of lapsed accounts.
When MobileMe started people could link, email-wise, their paid for .Mac accounts to the paid for MobileMe (@me.com) accounts.
Any @mac.com still works over the AIM service.
Now also @Me.com names worked - meaning some people had two valid AIM names - they are not liked for use with AIM just that the passwords will be the same.
With the end of MobileMe all those @me.com account died as far as AIM is concerned.
However you could link it to iCloud which effectively moved it to the iCloud server.
(i.e. they are iCloud issued @me.com ID instead of MobileMe ones)
Then Apple started to issue @icloud.com IDs
This could mean that some people have three working IDs for use with AIM (but all linked to one email Account at Apple).
NOTES
From Lion onwards (iChat 6 and Above) Apple have had the app also login in to Apple before it will allow the AIM Servers to "read" the password.
This applies to any iCloud issued ID - the "newer" iCloud linked @Me.com and @iCloud.com IDs
This means you cannot use those IDs in iChat 5 or earlier as those version only do an one point login only.
With the coming of iCloud other Apple IDs could be linked to iCloud which may have given you either @me.com and later an @iCloud.com ID as well or just an @icloud one if you were later to the party as it were.
Whilst in some cases this does give you two valid AIM Screen Name the originating Apple ID does not become one.
9:04 pm      Saturday; February 8, 2014
  iMac 2.5Ghz 5i 2011 (Mavericks 10.9)
 G4/1GhzDual MDD (Leopard 10.5.8)
 MacBookPro 2Gb (Snow Leopard 10.6.8)
 Mac OS X (10.6.8),
 Couple of iPhones and an iPad