The troubles continue for Acme Packet (NASDAQ:APKT), which provides hardware used in voice over IP applications.

The company, which on Thursday provided a Q2 earnings warning, is down sharply again Monday on a wave of negative Street commentary. The analysts covering Acme seem to be abandoning ship. In unison.

Piper Jaffray, J.P. Morgan and Cantor Fitzgerald have all downgraded the stock.

  • Piper Jaffray’s Troy Jensen cut his rating to Neutral from Buy; his price target drops to $5 from $11. “We still like APKT fropm a longer-term perspective, but concerns regarding telco weakness and lack of near-term catalysts could limit upside,” he writes.
  • J.P. Morgan’s Ehud Gelbaum dropped the stock to Underweight, from Overweight. He says demand for the company’s session border controllers “could be decelerating faster than either we or the company had been expecting.” He says it could take 1-2 quarters for Acme “to internalize a weaker demand environment,” and another 2-3 quarters “to realign the business.” Gelbaum cut his 2008 EPS estimate to 14 cents, from 32 cents. For 2009, he goes to 21 cents, from 40 cents.
  • Cantor Fitzgerald’s Edward Jackson cut his rating on the stock to Hold, from Buy, dropping his price target to $4.50 from $11. “Our experience suggests that technology companies that substantially miss financial forecasts typically enter periods of sustained under-performance,” he writes. “We suspect that the company’s common shares will have difficulty recovering for some time.”
  • ThinkPanmure’s Eric Kainer keeps his Buy rating on the stock, but cuts his price target to $8 from $15. He worries that a weaker environment for VoIP “will persist until the global economy improves, enterprises accelerate adoption of VoIP or a new catalyst arises.”

Both Jackson and Kainer note that the troubles at APKT have potentially negative ramifications for other providers of of VoIP infrastructure, including AudioCodes (NASDAQ:AUDC), Veraz Networks (VRAZ) and Sonus Networks (NASDAQ:SONS).

In Monday’s trading:

  • Acme Packet, which fell $3.16, or 40.6% on Thursday, is down another 4 cents, or 9.5%, to $4.18.
  • AudioCodes is down 7 cents, or 2%, to $3.38.
  • Veraz is down a penny, or 0.6%, to $1.58.
  • Sonus is down 4 cents, or 1.2%, to $3.19.