Texting on wi-fi | 7-Eleven Rates and Plans | Consumer forum

Sending and receiving texts normally uses your phone functionality, and is independent of the Internet, wi-fi, etc. So, yes, you will get charged for texts you send.
I think there are other messaging apps that use the Internet, which would give you text-like communication, but I'm not that familiar with those. (Maybe Google Hangouts? WhatsApp? Don't take my word for these... )

=== Right now, when I don't have a sim card I can send/receive as many texts as I want when I'm connected to wi-fi. ===
Can you explain how you are dong this?? What app or function of your phone are you using? Are you sending a text to another cell phone number? These "texts" you are talking about are probably not SMS text messages.

In the cell phone world, when people talk about "text messages", they are normally referring to SMS text messages. SMS text messages use the mobile phone infrastructure, and allow short messages to be sent from one mobile phone number to another mobile phone number. When cell phone providers talk about their texting packages/plans, they are talking about this text messaging system. Before the advent of smart phones and similar wi-fi connected devices, users of "dumb" cell phones commonly sent texts to one another by this method, and lots of people still use "unlimited texting" plans with their smart phones.
Since you have no SIM or phone number for your iPhone, you are not doing conventional SMS text messaging. Yes, you are probably using iMessage, and you are sending messages to another iMessage user, and you connect to one another by your email addresses (or something like that), and you are communicating by text with other users, but these are not "text messages" in the cell phone sense. You're just using your iPhone as a computer attached to the Internet by wi-fi, and your messages are exchanged over the Internet, and not via the cell phone infrastructure.
If you get a SIM card for your phone, you'll get a phone number. You will be able to send SMS text messages to another cell phone number, and sending each message will cost you 15 cents (unless you get some kind of text message package). If you wanted to use iMessage (or some other similar phone app that requires Internet access) when you are away from wi-fi, then you would require a data connection plan for your phone, which SpeakOut does offer.
The communication method you want to use will depend on what your friends and other contacts are using.
I hope that clears things up. Foe further details on what SpeakOut offers, check their web site.

Sending and receiving SMS text messages using your SIM card and phone number is a separate function from using iMessage to communicate using wi-fi/Internet and your email address. I don't know the iPhone, but you will be accessing the SMS text messaging function using a different icon/app from the one you use for iMessage. The SIM card will not cause your iMessage messages to be diverted through the SMS function. They are completely separate.

Remember that if you want to have a "real time" conversation with another person, they have to be actively watching whatever you're using:
- If you are connected to wi-fi, you can both use iMessage, for free.
- If you are away from wi-fi, then you can either use SMS messaging (which SpeakOut charges for), or use iMessage with your phone using cellular data (which also costs something).