Steve made the switch to an iPhone from his old Palm Pilot. The interface is very similar to the old Palm, but the iMessage app sometimes defaults to text message instead, charging him. Leo says that iMessage has never really worked right. There are internet only text messaging apps like Google Hangouts that he could use instead. There's also What's App, which also uses data. The addressee has to have a similar setup, though.
Pamela has a flip phone and her dad has an iPhone 4S. She tries to text, but it doesn't work right. Texts come out in gibberish. Leo says it's odd that the flipphone is messed up because SMS is good on all platforms. So that doesn't make any sense. Pam can use the iPod Touch if she has Wi-Fi access to do it. It only will work through Apple's iMessage, also. Pam can get other apps like What'sApp, Google Chat, or Skype, which all would handle messaging.
Steve bought an HTC Evo 4G with Virgin Mobile and he's having trouble with text messaging through Facebook. When his friend responds, it goes to his iPad, not his phone. Leo says that's probably because they're responding via iMessage. He'll have to delete his phone number from Facebook and then re-register the new one, even if it's the same number.
Annette bought a new iPhone 5 and she can't send pics to her friends running Android through text messages. Leo says that since Annette is using an iPhone on T-Mobile, the phone isn't configured right for iMessages, is getting confused and won't default to MMS. Here's a technote from T-Mobile. There's also a youtube video that will walk her through it called How To Fix MMS on iOS 6/6.0.1 iPhone 5/4S/4/3Gs Tmobile.
Leo says that would be a great option. There are some apps that could offer that, but Apple doesn't give third party access to the text message system. There are security issues in allowing third party access to text messaging, which is why Apple doesn't do that. Ray could jailbreak his iPhone to do that, but Leo doesn't recommend jailbreaking.
T Mobile offers something similar, but they don't carry the iPhone (yet). Android does have this, though. So if he's not married to the iPhone, he could switch to an Android phone.