How much does 1000 SMS messages cost? If it's actually significant I would grandfather them in at a lower rate per X number of messages and offer further discounts for referrals.
Most services I've seen in Europe are around €0.09 so "thousands" would mean upwards of €100. I've seen US providers go as low as $0.005 though.
I think the mistake is to have unlimited messages if messages are such a major cost factor. Most services with "unlimited X" have a soft and hard limit on X if you dig deeper. If you don't want to charge per usage (or for overages), you should do a mixed calculation based on typical and min/max usage per customer and how usage ebbs and flows over time.
For the grandfather plan I'd aim lower than that even if it means losing a little money on high use customers because their usage might decline in the future (at which point they're providing profit while being less likely to cancel because of FOMO) and because the lower price point and legacy will make them good multipliers, not just for direct referrals but also as references or partners for whitepapers.
Basically you can get more out of them than just money so treating them the same as later customers means missing out on that.
I think the mistake is to have unlimited messages if messages are such a major cost factor. Most services with "unlimited X" have a soft and hard limit on X if you dig deeper. If you don't want to charge per usage (or for overages), you should do a mixed calculation based on typical and min/max usage per customer and how usage ebbs and flows over time.
For the grandfather plan I'd aim lower than that even if it means losing a little money on high use customers because their usage might decline in the future (at which point they're providing profit while being less likely to cancel because of FOMO) and because the lower price point and legacy will make them good multipliers, not just for direct referrals but also as references or partners for whitepapers.
Basically you can get more out of them than just money so treating them the same as later customers means missing out on that.