There are a few different ways that you can call Taiwan from Thailand. You can use a traditional landline or mobile phone, or you can use a VoIP service.
If you want to use a traditional landline or mobile phone, you will need to find a Thai carrier that has a partnership with a Taiwanese carrier. There are a few different Thai carriers that have partnerships with Taiwanese carriers, so you should be able to find one that works for you.
If you want to use a VoIP service, there are a few different options that you can choose from. Skype is the most popular VoIP service, and it has a large number of users in Taiwan. There are also a few other VoIP services that have decent coverage in Taiwan, so you should be able to find one that works for you.