What are inexpensive SMS distribution services?

Question

SMS

Good afternoon. In an apartment building, the tenants decided to change the code, and as often happens, a war broke out between the activists and the code.
We need a tool to quickly notify all neighbors (about 300 numbers), and since this is all paid out of our own pocket, it means not expensive.
From the service you need:
1. A field where to write text
2. A field where to insert phone numbers in bulk (preferably all at once)
3. Low prices.
4. 100% SMS delivery.
Please advise.

Answer 1

Android phone with the ability to send SMS to groups + a SIM card with a tariff plan that has an included SMS package.
Or messengers. Viber or WhatsApp have group chats.

Answer 2

in Ukraine see sms.ua