Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
Using FaceTime and iMessage behind a firewall
iOS: About Messages
Set up iMessage
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
Unable to use FaceTime and iMessage with my apple ID
For non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8
How to Send SMS from iPad
Texas Mac Man, we seem to have the same hardware and ios. Maybe you can help direct me to a solution for a similar problem. I tried everything as best i could on the relevant support page, but I'm still stumped.
Problem: when attempting to sign in to either Facetime or Messages, this alert appears: "Could not sign in, please check your network connection and try again" when signing in to your Apple ID
Device affected: iPad2
Device NOT affected iPhone5C
I have not tried turning off Airplane mode, out of fear that it might lock in on my mobile carrier and may charge me for data use from the iPad... I upgraded to the iPhone plan and eliminated the iPad data only plaN, keeping it on airplane mode ever since.
1. The problem started after downloading and installing the latest iOS 8.1 for iPad.
2. I used this internet connection to download the iOS 8.1 update, and am now on Safari connected to the internet through this device to find out why Facetime won't work.
3. The wifi settings allowed the previous iOS to send/receive iMessages... And are sufficient to currently watch Netflix movies on this device... Given that iDevices don't change network settings from common use, and my iPhone can send iMessages while in airplane mode and on wifi, the settings must be correct.
4. I've successfully signed into my iTunes account on both my laptop and this device using the correct Apple email ID and password. I've successfully logged onto my Apple ID from the Apple website to confirm emails and IDs are verified, through Safari on this device.
5. My Apple ID is my current valid/alternate email address. I've signed into iCloud on both laptop and iPad using this password. I've emailed myself to and from my Apple ID email using this device. I've also tried signing into Facetime using my alternate Apple ID.
6. Time zone is correctly auto set to my nearest time zone town. When set manually, the problem is still present.
7. Cellular data connection is not subscribed for this device. This device with previous iOS has been able to use Messages through this wifi connection as it is currently configured. Attempts from various wifi/coffee spots to sign in using Apple ID and all possible alternates do not resolve the problem.
8. Even though this suggestion was not listed under this specific error message, I decided to try "waiting 24 hours" and the same error still results. It isn't clear if waiting means specifically not attempting to log in to iMessages.
I'll try waiting more and see where that gets me.