How do I use three way calling on my t-mobile phone?

I have the t-mobile W490 phone but I need to do a three way call I don't care how much it charges but my gram wants to talk to my boyfriend on the phone.How do I do a three way call. It would really help me if I knew howHow do I use three way calling on my t-mobile phone?to do a three way call you

1. call one person first wait for them to answer

2. when they answer hit the send button

3. dial the next person

4. hit the send button twice and their you go.