South African telecoms giant Vodacom plans to appeal against a court ruling that it massively increase the 47m rand ($2.5m; £2m) payout it has offered to the inventor of its Please Call Me texting service.

The Supreme Court of Appeal ruled in favour of Nkosana Makate after he rejected the offer in his long-running battle with the company for financial compensation for his lucrative idea.

The court ruled that Vodacom's offer was "inequitable". It ordered the company to give Mr Makate between 5% and 7.5% of the total revenue generated by the Please Call Me product over 18 years, plus interest.

The mybroadband.co.za tech site reported that the court also ordered Vodacom to use models presented by Mr Mokate's legal team to calculate the amount, meaning that he could be entitled to around 20bn rand.

In a statement, Vodacom said it was "surprised and disappointed" by the ruling, and it intended to challenge it in the Constitutional Court - the final court of appeal.

Two decades ago, Mr Makate, a former Vodacom financial manager, came up with the concept that went on to become the company's Please Call Me service, allowing customers to send a free message to another user on the same network requesting to be called back.

He entered into a verbal agreement with the company's then-director of product development and management, Philip Geissler, that he would get a share of the revenue generated by the product, triggering a dispute that remains unresolved.