Buy a 3G USB Modem?

[inquisitor]

If you have an Android phone with hotspot feature you indeed should question the use of a separate 3G modem. The only issue when using an Android phone as hotspot is the heat which most phones develop and from which the hardware may suffer over the time and also the battery wear caused by the high power consumption.

Personally I usually carry a mobile 3G hotspot from Huawei with me when I travel because I don't want to wear my Android phone too quickly and also I usually leave the SIM from my home network in it (as opposed to using a local SIM with lower data rates) so I remain reachable under my known phone number.
The advantage of these mobile hotspots is that you can use their internet connection from more than one device and that you can situate them freely so they have the best reception (on a window sill e.g.).
Huawei sell the following devices:

• E583x series (support 7.2 MBit/s DL and 5.76 MBit/s UL and hasn't a display but only colored LEDs, microSD is only accessible through USB) and further differ in the supported 3G frequencies:
  • E5830: 2100
  • E5832: 900/2100
  • E5838: 850/1900/2100
    
  
  
• E5832S/E585 (supports 7.2 MBit/s DL and 5.76 MBit/s UL, has a dotmarix display, microSD is accessible also through WiFi) and again exists with different frequency bands:
  • 900/2100
  • 850/900/2100
    
    
• E583C (supports 7.2 MBit/s DL and 5.76 MBit/s UL, has a dotmarix display and a connector for an external antenna, microSD is accessible also through WiFi) and comes in only one version:
  • 900/1900/2100
    
    
• E586 (supports HSPA+ with 21 MBit/s DL and has a dotmatrix display, microSD is accessible also through WiFi) which comes in only one frequency version so far:
  • 900/2100

You should make your choice depending on whether you like displays and on which 3G frequencies you require (depends on country and network operator).