Ionica Plc, the rapidly expanding Cambridge, UK-based radio telephony company, launched its initial public offering on the London stock exchange last week with the shares opening at 435 pence, well above the offer price of 390 pence. But the shares quickly fell to 419 pence, with six million shares traded in the first two hours, valuing the company at around 690m pounds. Chief executive Nigel Playford said that due to exceptionally strong demand, the offer had been priced the top end of the 370-390 pence window. The offer has raised net proceeds of 147m pounds for Ionica, which floated 24% of its equity, but none of Ionica’s existing shareholders have sold their stock. Private investors, who jumped on board earlier this year with a private placing of shares at 240 pence, are now sitting pretty. Ionica uses digital radio technology to connect residential telephones to a local exchange and thus has low connection costs. The company needs funds to expand its network. It also began trading in the US with American depository shares closing at $20.50 on Nasdaq Friday.