How to send short messages to mobile phones in Singapore on the Internet?

Because I am studying in Singapore and my boyfriend is in China, it is very expensive for him to contact me. I checked the free text messages for a long time, but it seems that there are none. There's only one way. But this is not a good idea. Do you know which company your friend's mobile phone service is from? There are three companies in Singapore. M 1, singtel, starhub, your friend's must be one of them. If you know the company, search official website of this company in Baidu or Google. There is a short message service or something. This kind of service can only be sent to our company by our company, which is a bit like China Mobile's Fetion. The mobile phone number of your lost friend, send him/her another one. (equivalent to sending it to yourself). The disadvantage of this method is that it cannot be replied.