lts a little bit trick to explain but in my own opinion l believe a router does improve reception if you have time to play with settings. l experimented this with a 3g wireless router plugged to PowerTel modem.
The very first thing and most important for me was issue of drivers and modem overheating. When you have 3G modem, you quickly clear the issue of drivers since the router only requires Dial number, no need for APN, username and password. For PowerTel, they use PAP authentication(you need to look for this in the router initiation logs as PowerTel will not provide you with such information)
Secondly, because there are no driver issue, the modem rarely overheats and is away from PC generated heat.
Thirdly, you can move the router about even putting on roof top of your house to gain better reception if you have wireless access from your PC or mobile phone.
After using the one which takes USB modems, l dont recommend it and yes you can still get the ones which takes any simcard, l will post results once l get one to test. lm in the process of getting one.
l have never bought one from Zimbabwe but you can search one from www.alibaba.com. They take pay-pal, western union, bank transfer and a lot and post to anywhere in the world since its located in China. You can also buy one or bulk from the manufacturers.
Good luck, hola me if you need more help!