What are the limitations with plans?

There is a Fair usage policy for paid plans that defines how much you can use the service for free.

FREE phone number
Premium plan includes one (1) free phone number per team member. Business plan includes five (5) free phone numbers per team member. Limitations apply.
FREE calls and call forwarding
Premium plan includes 2000 free minutes per user and month. Business plan includes 4000 free minutes per user and month.
All plans allow 1 concurrent outbound call per user. The capacity is pooled, so an account with 5 users can have up to 5 concurrent free outbound calls.
FREE Conference calls
Max 25 participants. Each user may only have one conference call at a time.
FREE Incoming calls on Sonetel phone numbers that are forwarded to VoIP devices.
One (1) concurrent call per phone number is free. Additional concurrent calls are charged $0.0075 per started minute for Premium plan and $0.0070 per started minute for the Business plan.
FREE Voice response
For Premium 20,000 usages per customer account and month and 50,000 usages per customer account and month for Business plan. Overuse is charged at $0.0075 per usage for Premium plan and $0.0070 per usage for the Business plan.
FREE Text-to-speech
Generate 500 free Text-to-speech recordings per month with Premium and 1,500 recordings with Business plan. Overuse is charged at $0.02 per minute started for Premium plan and $0.015 per minute started for the Business plan.
FREE Fax-to-email
1,000 faxes per Sonetel phone number and month.
FREE SMS-to-email
Premium plan includes 2,500 SMSs per Sonetel phone number and month. Business plan includes 5,000 SMSs per Sonetel phone number and month. Overuse is charged at $0.01 per message.
More free data storage
100 GB data storage per team member with the Premium plan. Business plan includes 1 TB data storage per user and month. Overuse is charged at $1 extra per month and started GB above the limit.

If you activate a paid plan after purchasing a phone number, then the free plan benefits with the number are activated after the number’s next renewal date.

You must maintain a positive prepaid balance to be able to make and forward free calls with paid plans.

The service is intended for normal individual business use and may not be used for telemarketing or mass-calling activities or any other unintended usage. Each user may only make one call at a time and max 8 hours of calls per day.

Extra charges: Sonetel reserves the right to charge extra for usage beyond the allowed usage levels and for usage that does not comply with the intended type of use at the following rates; Simultaneous incoming calls: $0.0070 per started minute on the Business plan and $0.0075 per started minute on Premium. Voice App: $0.0070 per usage for Business plan and $0.0075 per usage for Premium. Text-to-speech: $0.015 per started minute on Business plan and $0.02 per started minute on Premium. Conference calls: $0.05 per minute and participant. $0.01 per Fax-to-email and $0.01 per SMS-to-email. Call recording: $0.015 per started minute on Business plan and $0.02 per started minute on Premium plan. Sonetel reserves the right to adjust these terms.