Troubleshooting iPad 2

I bought ipad 2 second hand. it doe have a dialer.l am not receiving calls and sms. When I try to text someon,it says he/she isn't registered on iMessage. to buy data bundles,l have to take the sim card into another phone.l downloaded Optima dialer but requires me to put operator code,username and password. I put the operator code and the carrier's name as username but the password l don't know. I put my icloud password but the dial is taking long initiallisin. When l try to dial numbe,it says check internet and registration.l downloaded about 2 more dialers but they are the same.l want to open an account on Twitter and viber but the messages with verification codes are not reaching me. l am not receiving any. I am totally frustrated. Please help.