Sending a birthday invitation to everyone at once
Pick a plan, name the party, and write the message. One dollar covers 25 guests and five dollars covers 100 for that message, with no account to create and no monthly fee afterwards.
You then get a sign-up link and a QR code. Send that link to the people you want at the party, or put the QR code on a flyer at the school gate. Guests tap it and add their own number. Nobody gets texted who did not opt in, which is what keeps this legal and also what stops the awkward wrong-number moments.
On the date you chose, at 12pm Eastern, everyone receives the same message individually. It looks like a normal text from a normal number, not a group thread.
Kids' parties: you are really inviting the parents
For anyone under about thirteen, the invitation goes to a parent, not the child. That single fact changes how you collect numbers. You are not gathering a class list of kids, you are gathering a list of adults who will be doing the driving.
The easiest route is the class WhatsApp group or the room parent, who usually already has everyone. Post your sign-up link there once and let parents opt in themselves. That way you are not chasing individual numbers and you are not storing a list of contacts you got second hand.
A QR code on the paper invitation works too, if the school still sends bags home. Parents scan it, and now you can reach all of them at once when the venue changes or the party runs late.
Milestone birthdays and surprises
A fortieth or a sixtieth has a different problem. The guest list is spread across old friends, work people and family, and half of them are not in any shared group chat. A sign-up link solves that because you can drop it into several different places at once and it all lands in one list.
For a surprise, the important detail is that the person being surprised never sees the sign-up link. Everyone who does sign up gets private one-to-one messages, so there is no group thread for them to stumble across on a shared iPad.
If you need to send more than one message, say the invitation now and a reminder the week before, each one is a separate send at the same plan price. Scheduling a text in advance covers how the timing works.
What the invitation should actually say
You have about 160 characters, so lead with the four things people need: whose birthday, what date, what time, and where. Everything else is optional.
A working example: SOPHIE TURNS 7: Sat March 14, 2pm to 4pm, Riverside Park pavilion. Pizza and cake. Text back if you can come.
Skip the long preamble. People read a text in two seconds and decide whether they are free. If there is more detail, like parking or a gift registry, put it in a second message closer to the day rather than cramming it in.
When paper is still the better call
Text invitations are not always right. A first birthday, a christening tied to the party, or a milestone where the invitation itself is a keepsake all justify paper. Older relatives who do not text are also a real consideration, and there is no clever workaround for that.
The honest split most people land on is paper for the ten people who would appreciate it and a text for the other thirty who just need the details. If your guest list is mostly the second group, the cost math across different guest counts is worth a look before you commit.