This is an interesting idea. I looked into this before when I was traveling internationally, but I ran into issues when trying to set it up with services like Twilio.

1. Many companies send from SHORT code numbers, and not all VOIP providers can accept them.

2. Many companies will look up the number type and only send to cellphone numbers.

3. If you use a SIM modem, some phone companies will check the IMEI and terminate your contract if it's not in a cellphone.