TPG shareholders have delivered a brutal verdict on its almost $1.3 billion splurge buying up 4G mobile spectrum to build a new mobile network wiping one-fifth from the company's share price in a single day.

The broadband internet and mobile provider last week agreed to pay $1.26 billion for a chunk of the nation's 4G mobile spectrum and revealed it would spend another $600 million building a mobile network to rival those operated by Telstra, Optus and Vodafone.

TPG entered a trading halt last Wednesday, prior to the announcement, and detailed a $400 million share entitlement offer to fund construction of the new network.

Upon returning to trade on Tuesday morning, TPG shares plunged immediately. From a close of $6.54 per share before it entered the trading halt, TPG shares had dived to $5.42 by midday Tuesday - a drop of 17.8 per cent - before closing at $5.50. Over one billion dollars was wiped from TPG's market value, falling from $5.54 billion to $4.42 billion.