Seeking guidance with Airport Express and VOIP

I currently use a Linksys Wireless G broadband router with 2 phone ports.

I use this to dish up my wifi as well as provide VOIP service for my landline.

So it goes:

Cable modem--->Wireless G router---->Telephone

Same Wireless G router--->Wifi

What I was trying to do is to expand at least the coverage and hopefully also the speed of my wifi.

So two questions:

1) can an airport express "hook" into this set up and extend coverage? and

2) would it improve speeds?

Thanks in advance.