Short answer: No.
The Gizmo press release just says that Gizmo and Google Talk users can IM each other. That's no big deal. You can connect Google talk to AIM, MSN, and Yahoo already. This is why open standards work. Everyone seems amazed, but this should have all happened years ago. I like Larry Page's quote during his 2006 CES keynote:
You can email anyone, but you can't instant message anyone. Guess which was developed at universities.
Getting back to what I was talking about, though, what will happen to the likes of Skype and Gizmo. They'll just be fused in. Probably become irrelevant as everyone will just use thier respective already established IM clients to call one another, setup conference calls, call regular land lines, etc. IM clients will slip into VoIP handsets and cell phones, etc. Just look at Google's two proposed extensions to XMPP – JEP-0166: Jingle Signalling and JEP-0167: Jingle Audio – that seek to standardize how to send multimedia (such as audio) over Jabber.
But here is the big one: Jabphone
Jabphone allows you to call your friends on the phone using the Jabber Instant Messaging system.
Found via O'Reilly Radar with this quote:
The Poly9 hackers who were at Where 2.0 in 2005, showed up at Emerging Telephony today with Jabphone, a service built on libjingle, Jabber, and Asterisk that lets you call out to regular telephone numbers from Google Talk. This is the power of open standards and open source, folks--they've been able to add the Skype Out feature to Google Talk without any assistance from Google. You can't do that with Skype, Yahoo Messenger with Voice, or MSN Messenger. I don't know what blows me away more--that these guys are so creative in two very different areas, or that they have another surprise up their sleeve to show off at the ETel Fair tomorrow night